Organic LEDs ndash part 7
bull Solvation Effect ndash Review
bull Solid State Solvation
bull Exciton Dynamics in Disordered Organic Thin Films
bull Quantum Dot LEDs
Handout on QD-LEDs Coe et al Nature 420 800 (2002)
April 29 2003 ndash Organic Optoelectronics - Lecture 20
Electroluminescence in Doped Organic Films
1Excitons formed
from combinationof electrons and
holes
2Excitons transfer to
luminescent dye
Electroluminescence of x DCM2 in Alq3 OLEDs
1048790 solvation is a physical perturbation of lumophorersquos molecular states1048790 isolated molecule (in a gas phase) and solvated molecule are in the same chemical state(no solvent induced proton or electron transfer ionization complexation isomerization)
change in the spectral position of aborption luminescence band
due to change in the polarity of the medium
Solid State Solvation (SSS)
polarlumophor
e
dipolar hostwith moment μ
ldquoself polarizationrdquofor strongly dipolar lumophores
(aggregation possible for highly polar molecules)
solute (chromophore)WITH DIPOLE MOMENT μ
solvent
Bathochromic (red) PL shiftHypsochromic (blue) PL shift
Influence of μ0 and μ1
on Chromatic Shift Direction
PL of DCM2 Solutions and Thin Film
Bulović et al Chem Phys Lett 287 455 (1998)
Excited State(non-
equilibrium)
Excited State(equilibrium)
Ground State(equilibrium)
Ground State(non-equilibrium)
Dynamic Relaxation Picture (aka solvation)
1 DCM2 in Alq3
1 DCM2 in Zrq4
polar hostμ ~ 55 D
non-polar host
Thin Film Photoluminescence
A ldquoCleanerrdquo Experiment
bull Employ trace DCM2 so as to effectively eliminate aggregation
bull But still appreciably change local medium use rArr another dopant
bull should be polar and optically inactive (ie wide band gap)
CA Doping and Electronic Susceptibility
42 nm red shift from 0 to 25 CA
Results unchanged even for 10x
higher DCM2 concentration
DCM2 aggregation not the answer
Local fields are responsible for thespectral shiftshellip
hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect
Peak PL Energy of PSCADCM2 Films
Bulk Electronic Susceptibility of PSCADCM2 Films
Solvation TheoryDynamic Relaxation Picture (aka solvation)
Excited State(non-
equilibrium)
Excited State(equilibrium)
Ground State(equilibrium)
Ground State(non-
equilibrium)
Connecting Theory to Experiment
constant with CA n nearly constant with CA(ranging from ~155 to ~165)
Exciton Dynamics in Time Dependant PL
Dynamic Spectral Shifts of DCM2 in Alq3
bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)
~ DCM2 PL red shifts gt 20 nm over 6 ns ~
Wavelength [ nm ]
Time Evolution of 4 DCM2 in Alq3 PL Spectrum
Electronic Processes in Molecules
density of availableS1 or T1 states
Time Evolution of DCM2 Solution PL Spectra
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
Excitonic Energy Variations
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Electroluminescence in Doped Organic Films
1Excitons formed
from combinationof electrons and
holes
2Excitons transfer to
luminescent dye
Electroluminescence of x DCM2 in Alq3 OLEDs
1048790 solvation is a physical perturbation of lumophorersquos molecular states1048790 isolated molecule (in a gas phase) and solvated molecule are in the same chemical state(no solvent induced proton or electron transfer ionization complexation isomerization)
change in the spectral position of aborption luminescence band
due to change in the polarity of the medium
Solid State Solvation (SSS)
polarlumophor
e
dipolar hostwith moment μ
ldquoself polarizationrdquofor strongly dipolar lumophores
(aggregation possible for highly polar molecules)
solute (chromophore)WITH DIPOLE MOMENT μ
solvent
Bathochromic (red) PL shiftHypsochromic (blue) PL shift
Influence of μ0 and μ1
on Chromatic Shift Direction
PL of DCM2 Solutions and Thin Film
Bulović et al Chem Phys Lett 287 455 (1998)
Excited State(non-
equilibrium)
Excited State(equilibrium)
Ground State(equilibrium)
Ground State(non-equilibrium)
Dynamic Relaxation Picture (aka solvation)
1 DCM2 in Alq3
1 DCM2 in Zrq4
polar hostμ ~ 55 D
non-polar host
Thin Film Photoluminescence
A ldquoCleanerrdquo Experiment
bull Employ trace DCM2 so as to effectively eliminate aggregation
bull But still appreciably change local medium use rArr another dopant
bull should be polar and optically inactive (ie wide band gap)
CA Doping and Electronic Susceptibility
42 nm red shift from 0 to 25 CA
Results unchanged even for 10x
higher DCM2 concentration
DCM2 aggregation not the answer
Local fields are responsible for thespectral shiftshellip
hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect
Peak PL Energy of PSCADCM2 Films
Bulk Electronic Susceptibility of PSCADCM2 Films
Solvation TheoryDynamic Relaxation Picture (aka solvation)
Excited State(non-
equilibrium)
Excited State(equilibrium)
Ground State(equilibrium)
Ground State(non-
equilibrium)
Connecting Theory to Experiment
constant with CA n nearly constant with CA(ranging from ~155 to ~165)
Exciton Dynamics in Time Dependant PL
Dynamic Spectral Shifts of DCM2 in Alq3
bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)
~ DCM2 PL red shifts gt 20 nm over 6 ns ~
Wavelength [ nm ]
Time Evolution of 4 DCM2 in Alq3 PL Spectrum
Electronic Processes in Molecules
density of availableS1 or T1 states
Time Evolution of DCM2 Solution PL Spectra
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
Excitonic Energy Variations
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Electroluminescence of x DCM2 in Alq3 OLEDs
1048790 solvation is a physical perturbation of lumophorersquos molecular states1048790 isolated molecule (in a gas phase) and solvated molecule are in the same chemical state(no solvent induced proton or electron transfer ionization complexation isomerization)
change in the spectral position of aborption luminescence band
due to change in the polarity of the medium
Solid State Solvation (SSS)
polarlumophor
e
dipolar hostwith moment μ
ldquoself polarizationrdquofor strongly dipolar lumophores
(aggregation possible for highly polar molecules)
solute (chromophore)WITH DIPOLE MOMENT μ
solvent
Bathochromic (red) PL shiftHypsochromic (blue) PL shift
Influence of μ0 and μ1
on Chromatic Shift Direction
PL of DCM2 Solutions and Thin Film
Bulović et al Chem Phys Lett 287 455 (1998)
Excited State(non-
equilibrium)
Excited State(equilibrium)
Ground State(equilibrium)
Ground State(non-equilibrium)
Dynamic Relaxation Picture (aka solvation)
1 DCM2 in Alq3
1 DCM2 in Zrq4
polar hostμ ~ 55 D
non-polar host
Thin Film Photoluminescence
A ldquoCleanerrdquo Experiment
bull Employ trace DCM2 so as to effectively eliminate aggregation
bull But still appreciably change local medium use rArr another dopant
bull should be polar and optically inactive (ie wide band gap)
CA Doping and Electronic Susceptibility
42 nm red shift from 0 to 25 CA
Results unchanged even for 10x
higher DCM2 concentration
DCM2 aggregation not the answer
Local fields are responsible for thespectral shiftshellip
hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect
Peak PL Energy of PSCADCM2 Films
Bulk Electronic Susceptibility of PSCADCM2 Films
Solvation TheoryDynamic Relaxation Picture (aka solvation)
Excited State(non-
equilibrium)
Excited State(equilibrium)
Ground State(equilibrium)
Ground State(non-
equilibrium)
Connecting Theory to Experiment
constant with CA n nearly constant with CA(ranging from ~155 to ~165)
Exciton Dynamics in Time Dependant PL
Dynamic Spectral Shifts of DCM2 in Alq3
bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)
~ DCM2 PL red shifts gt 20 nm over 6 ns ~
Wavelength [ nm ]
Time Evolution of 4 DCM2 in Alq3 PL Spectrum
Electronic Processes in Molecules
density of availableS1 or T1 states
Time Evolution of DCM2 Solution PL Spectra
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
Excitonic Energy Variations
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
1048790 solvation is a physical perturbation of lumophorersquos molecular states1048790 isolated molecule (in a gas phase) and solvated molecule are in the same chemical state(no solvent induced proton or electron transfer ionization complexation isomerization)
change in the spectral position of aborption luminescence band
due to change in the polarity of the medium
Solid State Solvation (SSS)
polarlumophor
e
dipolar hostwith moment μ
ldquoself polarizationrdquofor strongly dipolar lumophores
(aggregation possible for highly polar molecules)
solute (chromophore)WITH DIPOLE MOMENT μ
solvent
Bathochromic (red) PL shiftHypsochromic (blue) PL shift
Influence of μ0 and μ1
on Chromatic Shift Direction
PL of DCM2 Solutions and Thin Film
Bulović et al Chem Phys Lett 287 455 (1998)
Excited State(non-
equilibrium)
Excited State(equilibrium)
Ground State(equilibrium)
Ground State(non-equilibrium)
Dynamic Relaxation Picture (aka solvation)
1 DCM2 in Alq3
1 DCM2 in Zrq4
polar hostμ ~ 55 D
non-polar host
Thin Film Photoluminescence
A ldquoCleanerrdquo Experiment
bull Employ trace DCM2 so as to effectively eliminate aggregation
bull But still appreciably change local medium use rArr another dopant
bull should be polar and optically inactive (ie wide band gap)
CA Doping and Electronic Susceptibility
42 nm red shift from 0 to 25 CA
Results unchanged even for 10x
higher DCM2 concentration
DCM2 aggregation not the answer
Local fields are responsible for thespectral shiftshellip
hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect
Peak PL Energy of PSCADCM2 Films
Bulk Electronic Susceptibility of PSCADCM2 Films
Solvation TheoryDynamic Relaxation Picture (aka solvation)
Excited State(non-
equilibrium)
Excited State(equilibrium)
Ground State(equilibrium)
Ground State(non-
equilibrium)
Connecting Theory to Experiment
constant with CA n nearly constant with CA(ranging from ~155 to ~165)
Exciton Dynamics in Time Dependant PL
Dynamic Spectral Shifts of DCM2 in Alq3
bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)
~ DCM2 PL red shifts gt 20 nm over 6 ns ~
Wavelength [ nm ]
Time Evolution of 4 DCM2 in Alq3 PL Spectrum
Electronic Processes in Molecules
density of availableS1 or T1 states
Time Evolution of DCM2 Solution PL Spectra
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
Excitonic Energy Variations
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Solid State Solvation (SSS)
polarlumophor
e
dipolar hostwith moment μ
ldquoself polarizationrdquofor strongly dipolar lumophores
(aggregation possible for highly polar molecules)
solute (chromophore)WITH DIPOLE MOMENT μ
solvent
Bathochromic (red) PL shiftHypsochromic (blue) PL shift
Influence of μ0 and μ1
on Chromatic Shift Direction
PL of DCM2 Solutions and Thin Film
Bulović et al Chem Phys Lett 287 455 (1998)
Excited State(non-
equilibrium)
Excited State(equilibrium)
Ground State(equilibrium)
Ground State(non-equilibrium)
Dynamic Relaxation Picture (aka solvation)
1 DCM2 in Alq3
1 DCM2 in Zrq4
polar hostμ ~ 55 D
non-polar host
Thin Film Photoluminescence
A ldquoCleanerrdquo Experiment
bull Employ trace DCM2 so as to effectively eliminate aggregation
bull But still appreciably change local medium use rArr another dopant
bull should be polar and optically inactive (ie wide band gap)
CA Doping and Electronic Susceptibility
42 nm red shift from 0 to 25 CA
Results unchanged even for 10x
higher DCM2 concentration
DCM2 aggregation not the answer
Local fields are responsible for thespectral shiftshellip
hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect
Peak PL Energy of PSCADCM2 Films
Bulk Electronic Susceptibility of PSCADCM2 Films
Solvation TheoryDynamic Relaxation Picture (aka solvation)
Excited State(non-
equilibrium)
Excited State(equilibrium)
Ground State(equilibrium)
Ground State(non-
equilibrium)
Connecting Theory to Experiment
constant with CA n nearly constant with CA(ranging from ~155 to ~165)
Exciton Dynamics in Time Dependant PL
Dynamic Spectral Shifts of DCM2 in Alq3
bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)
~ DCM2 PL red shifts gt 20 nm over 6 ns ~
Wavelength [ nm ]
Time Evolution of 4 DCM2 in Alq3 PL Spectrum
Electronic Processes in Molecules
density of availableS1 or T1 states
Time Evolution of DCM2 Solution PL Spectra
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
Excitonic Energy Variations
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
solute (chromophore)WITH DIPOLE MOMENT μ
solvent
Bathochromic (red) PL shiftHypsochromic (blue) PL shift
Influence of μ0 and μ1
on Chromatic Shift Direction
PL of DCM2 Solutions and Thin Film
Bulović et al Chem Phys Lett 287 455 (1998)
Excited State(non-
equilibrium)
Excited State(equilibrium)
Ground State(equilibrium)
Ground State(non-equilibrium)
Dynamic Relaxation Picture (aka solvation)
1 DCM2 in Alq3
1 DCM2 in Zrq4
polar hostμ ~ 55 D
non-polar host
Thin Film Photoluminescence
A ldquoCleanerrdquo Experiment
bull Employ trace DCM2 so as to effectively eliminate aggregation
bull But still appreciably change local medium use rArr another dopant
bull should be polar and optically inactive (ie wide band gap)
CA Doping and Electronic Susceptibility
42 nm red shift from 0 to 25 CA
Results unchanged even for 10x
higher DCM2 concentration
DCM2 aggregation not the answer
Local fields are responsible for thespectral shiftshellip
hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect
Peak PL Energy of PSCADCM2 Films
Bulk Electronic Susceptibility of PSCADCM2 Films
Solvation TheoryDynamic Relaxation Picture (aka solvation)
Excited State(non-
equilibrium)
Excited State(equilibrium)
Ground State(equilibrium)
Ground State(non-
equilibrium)
Connecting Theory to Experiment
constant with CA n nearly constant with CA(ranging from ~155 to ~165)
Exciton Dynamics in Time Dependant PL
Dynamic Spectral Shifts of DCM2 in Alq3
bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)
~ DCM2 PL red shifts gt 20 nm over 6 ns ~
Wavelength [ nm ]
Time Evolution of 4 DCM2 in Alq3 PL Spectrum
Electronic Processes in Molecules
density of availableS1 or T1 states
Time Evolution of DCM2 Solution PL Spectra
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
Excitonic Energy Variations
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
PL of DCM2 Solutions and Thin Film
Bulović et al Chem Phys Lett 287 455 (1998)
Excited State(non-
equilibrium)
Excited State(equilibrium)
Ground State(equilibrium)
Ground State(non-equilibrium)
Dynamic Relaxation Picture (aka solvation)
1 DCM2 in Alq3
1 DCM2 in Zrq4
polar hostμ ~ 55 D
non-polar host
Thin Film Photoluminescence
A ldquoCleanerrdquo Experiment
bull Employ trace DCM2 so as to effectively eliminate aggregation
bull But still appreciably change local medium use rArr another dopant
bull should be polar and optically inactive (ie wide band gap)
CA Doping and Electronic Susceptibility
42 nm red shift from 0 to 25 CA
Results unchanged even for 10x
higher DCM2 concentration
DCM2 aggregation not the answer
Local fields are responsible for thespectral shiftshellip
hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect
Peak PL Energy of PSCADCM2 Films
Bulk Electronic Susceptibility of PSCADCM2 Films
Solvation TheoryDynamic Relaxation Picture (aka solvation)
Excited State(non-
equilibrium)
Excited State(equilibrium)
Ground State(equilibrium)
Ground State(non-
equilibrium)
Connecting Theory to Experiment
constant with CA n nearly constant with CA(ranging from ~155 to ~165)
Exciton Dynamics in Time Dependant PL
Dynamic Spectral Shifts of DCM2 in Alq3
bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)
~ DCM2 PL red shifts gt 20 nm over 6 ns ~
Wavelength [ nm ]
Time Evolution of 4 DCM2 in Alq3 PL Spectrum
Electronic Processes in Molecules
density of availableS1 or T1 states
Time Evolution of DCM2 Solution PL Spectra
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
Excitonic Energy Variations
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Excited State(non-
equilibrium)
Excited State(equilibrium)
Ground State(equilibrium)
Ground State(non-equilibrium)
Dynamic Relaxation Picture (aka solvation)
1 DCM2 in Alq3
1 DCM2 in Zrq4
polar hostμ ~ 55 D
non-polar host
Thin Film Photoluminescence
A ldquoCleanerrdquo Experiment
bull Employ trace DCM2 so as to effectively eliminate aggregation
bull But still appreciably change local medium use rArr another dopant
bull should be polar and optically inactive (ie wide band gap)
CA Doping and Electronic Susceptibility
42 nm red shift from 0 to 25 CA
Results unchanged even for 10x
higher DCM2 concentration
DCM2 aggregation not the answer
Local fields are responsible for thespectral shiftshellip
hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect
Peak PL Energy of PSCADCM2 Films
Bulk Electronic Susceptibility of PSCADCM2 Films
Solvation TheoryDynamic Relaxation Picture (aka solvation)
Excited State(non-
equilibrium)
Excited State(equilibrium)
Ground State(equilibrium)
Ground State(non-
equilibrium)
Connecting Theory to Experiment
constant with CA n nearly constant with CA(ranging from ~155 to ~165)
Exciton Dynamics in Time Dependant PL
Dynamic Spectral Shifts of DCM2 in Alq3
bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)
~ DCM2 PL red shifts gt 20 nm over 6 ns ~
Wavelength [ nm ]
Time Evolution of 4 DCM2 in Alq3 PL Spectrum
Electronic Processes in Molecules
density of availableS1 or T1 states
Time Evolution of DCM2 Solution PL Spectra
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
Excitonic Energy Variations
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
1 DCM2 in Alq3
1 DCM2 in Zrq4
polar hostμ ~ 55 D
non-polar host
Thin Film Photoluminescence
A ldquoCleanerrdquo Experiment
bull Employ trace DCM2 so as to effectively eliminate aggregation
bull But still appreciably change local medium use rArr another dopant
bull should be polar and optically inactive (ie wide band gap)
CA Doping and Electronic Susceptibility
42 nm red shift from 0 to 25 CA
Results unchanged even for 10x
higher DCM2 concentration
DCM2 aggregation not the answer
Local fields are responsible for thespectral shiftshellip
hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect
Peak PL Energy of PSCADCM2 Films
Bulk Electronic Susceptibility of PSCADCM2 Films
Solvation TheoryDynamic Relaxation Picture (aka solvation)
Excited State(non-
equilibrium)
Excited State(equilibrium)
Ground State(equilibrium)
Ground State(non-
equilibrium)
Connecting Theory to Experiment
constant with CA n nearly constant with CA(ranging from ~155 to ~165)
Exciton Dynamics in Time Dependant PL
Dynamic Spectral Shifts of DCM2 in Alq3
bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)
~ DCM2 PL red shifts gt 20 nm over 6 ns ~
Wavelength [ nm ]
Time Evolution of 4 DCM2 in Alq3 PL Spectrum
Electronic Processes in Molecules
density of availableS1 or T1 states
Time Evolution of DCM2 Solution PL Spectra
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
Excitonic Energy Variations
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
A ldquoCleanerrdquo Experiment
bull Employ trace DCM2 so as to effectively eliminate aggregation
bull But still appreciably change local medium use rArr another dopant
bull should be polar and optically inactive (ie wide band gap)
CA Doping and Electronic Susceptibility
42 nm red shift from 0 to 25 CA
Results unchanged even for 10x
higher DCM2 concentration
DCM2 aggregation not the answer
Local fields are responsible for thespectral shiftshellip
hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect
Peak PL Energy of PSCADCM2 Films
Bulk Electronic Susceptibility of PSCADCM2 Films
Solvation TheoryDynamic Relaxation Picture (aka solvation)
Excited State(non-
equilibrium)
Excited State(equilibrium)
Ground State(equilibrium)
Ground State(non-
equilibrium)
Connecting Theory to Experiment
constant with CA n nearly constant with CA(ranging from ~155 to ~165)
Exciton Dynamics in Time Dependant PL
Dynamic Spectral Shifts of DCM2 in Alq3
bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)
~ DCM2 PL red shifts gt 20 nm over 6 ns ~
Wavelength [ nm ]
Time Evolution of 4 DCM2 in Alq3 PL Spectrum
Electronic Processes in Molecules
density of availableS1 or T1 states
Time Evolution of DCM2 Solution PL Spectra
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
Excitonic Energy Variations
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
CA Doping and Electronic Susceptibility
42 nm red shift from 0 to 25 CA
Results unchanged even for 10x
higher DCM2 concentration
DCM2 aggregation not the answer
Local fields are responsible for thespectral shiftshellip
hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect
Peak PL Energy of PSCADCM2 Films
Bulk Electronic Susceptibility of PSCADCM2 Films
Solvation TheoryDynamic Relaxation Picture (aka solvation)
Excited State(non-
equilibrium)
Excited State(equilibrium)
Ground State(equilibrium)
Ground State(non-
equilibrium)
Connecting Theory to Experiment
constant with CA n nearly constant with CA(ranging from ~155 to ~165)
Exciton Dynamics in Time Dependant PL
Dynamic Spectral Shifts of DCM2 in Alq3
bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)
~ DCM2 PL red shifts gt 20 nm over 6 ns ~
Wavelength [ nm ]
Time Evolution of 4 DCM2 in Alq3 PL Spectrum
Electronic Processes in Molecules
density of availableS1 or T1 states
Time Evolution of DCM2 Solution PL Spectra
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
Excitonic Energy Variations
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Solvation TheoryDynamic Relaxation Picture (aka solvation)
Excited State(non-
equilibrium)
Excited State(equilibrium)
Ground State(equilibrium)
Ground State(non-
equilibrium)
Connecting Theory to Experiment
constant with CA n nearly constant with CA(ranging from ~155 to ~165)
Exciton Dynamics in Time Dependant PL
Dynamic Spectral Shifts of DCM2 in Alq3
bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)
~ DCM2 PL red shifts gt 20 nm over 6 ns ~
Wavelength [ nm ]
Time Evolution of 4 DCM2 in Alq3 PL Spectrum
Electronic Processes in Molecules
density of availableS1 or T1 states
Time Evolution of DCM2 Solution PL Spectra
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
Excitonic Energy Variations
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Connecting Theory to Experiment
constant with CA n nearly constant with CA(ranging from ~155 to ~165)
Exciton Dynamics in Time Dependant PL
Dynamic Spectral Shifts of DCM2 in Alq3
bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)
~ DCM2 PL red shifts gt 20 nm over 6 ns ~
Wavelength [ nm ]
Time Evolution of 4 DCM2 in Alq3 PL Spectrum
Electronic Processes in Molecules
density of availableS1 or T1 states
Time Evolution of DCM2 Solution PL Spectra
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
Excitonic Energy Variations
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Exciton Dynamics in Time Dependant PL
Dynamic Spectral Shifts of DCM2 in Alq3
bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)
~ DCM2 PL red shifts gt 20 nm over 6 ns ~
Wavelength [ nm ]
Time Evolution of 4 DCM2 in Alq3 PL Spectrum
Electronic Processes in Molecules
density of availableS1 or T1 states
Time Evolution of DCM2 Solution PL Spectra
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
Excitonic Energy Variations
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Dynamic Spectral Shifts of DCM2 in Alq3
bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)
~ DCM2 PL red shifts gt 20 nm over 6 ns ~
Wavelength [ nm ]
Time Evolution of 4 DCM2 in Alq3 PL Spectrum
Electronic Processes in Molecules
density of availableS1 or T1 states
Time Evolution of DCM2 Solution PL Spectra
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
Excitonic Energy Variations
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Time Evolution of 4 DCM2 in Alq3 PL Spectrum
Electronic Processes in Molecules
density of availableS1 or T1 states
Time Evolution of DCM2 Solution PL Spectra
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
Excitonic Energy Variations
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Electronic Processes in Molecules
density of availableS1 or T1 states
Time Evolution of DCM2 Solution PL Spectra
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
Excitonic Energy Variations
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Time Evolution of DCM2 Solution PL Spectra
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
Excitonic Energy Variations
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
Excitonic Energy Variations
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Excitonic Energy Variations
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Time Evolution of Peak PL in Neat Thin Films
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Parameters for Simulating Exciton Diffusion
observed radiative lifetime (τ)No
rmal
ized
Inte
grat
ed Sp
ectr
al In
tens
ity
Foumlrster radius (RF) Assign value for allowed transfers
Assume Gaussian shape of width wDOS
Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip
excitonic density of states (gex(E))
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Fitting Simulation to Experiment ndash Doped Films
bull Good fits possible for all data sets
bull RF decreases with increasing doping falling from 52 Aring to 22 Aring
bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Fitting Simulation ndash Neat Films
bull Spectral shift observed in each material system
bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion
bull Even with no dipole some dispersion exists
bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Temporal Solid State Solvation
upon excitation both magnitude and direction
of lumophore dipole moment can change
FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~
following the excitation the environment surrounding the
excited molecule will reorganize to minimize the overall
energy of the system (maximize micro bull Eloc)
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Molecular Reconfiguration ~
DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES
log(Time)
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Fusion of Two Material Sets Hybrid devicescould enable
LEDs Solar CellsPhotodetectorsModulators and
Lasers
which utilize thebest properties of each individual material
Efficient
OrganicSemiconductors
Flexible
Emissive
Fabrication ofrational
structureshas been the
mainobstacle to date
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Fusion of Two Material Sets
Quantum Dots Organic Molecules
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors
ZnS overcoating shell(0 to 5 monolayers)
Oleic Acid orTOPO capsSynthetic routes of Murray et
al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102
Trioctylphosphine oxide
Tris(8-hydroxyquinoline)Aluminum (III)
3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole
NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine
NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres
Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs
Phase segregation is driven by acombination of size and
chemistry
Phase Segregation and Self-Assembly
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Design of Device StructuresQDs are poor chargetransport materials
Isolate layer functions of maximizedevice performance1 Generate excitons on organic
sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence
Phase Segregation
But efficient emittershellip
Use organics for charge transport
Need a new fabrication method inorder to be able to make such doubleheterostructures
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
A general method
Phase segregation occurs for different
1) organic hosts TPDNPD and poly-TPD
2) solvents chloroformchlorobenzene andmixtures with toluene
3) QD core materialsPbSe CdSe andCdSe(ZnS)
4) QD capping moleculesoleic acid and TOPO
5) QD core size 4-8nm
6) substrates SiliconGlass ITO
7) Spin parametersspeed accelerationand time
bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Spectral Dependence on Current Density
TOP DOWN VIEW of the QD MONOLAYER
Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed
CROSS-SECTIONAL VIEW of QD-LED
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Benefits of Quantum Dots in Organic LEDs
Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs
possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes
The ideal dye molecule
Top Related