Electronic and Optoelectronic Polymers
Wen-Chang ChenDepartment of Chemical Engineering
Institute of Polymer Science and Engineering
National Taiwan University
History of Conjugated Polymers
Electronic Structures of Conjugated Polymers
Polymer Light-emitting Diodes
Polymer-based Thin Film (or Field Effect) Transistors
Polymer-based Photovoltaics
Polymers for Memory devices
Outlines
What’s Transistor?
Transistor
A device composed of semiconductor materials that amplifiers a signal or opens or close circuit.
The key ingredient of all digital circuits, including computers. Today’s microprocessors contains tens of millions of microscopic transistors.
Field-Effect Transistor
A voltage applied between the gate and drain controls the current flowing between the source and drain
What’s Transistor?
Field effect transistor works like a drain
Organic Thin Film Transistors (OTFTs)
Organic transistors are transistors that use organic molecules rather than silicon for their active materials. These active materials can be composed of a wide variety of molecules.
Compatibility with plastic substances Lower-cost deposition process such as
spin coating, printing, evaporation Lower temperature manufacturing
(60-120oC)
Advantages
Disadvantages Lower mobility and switching speeds compared to
silicon wafers
Subjects of the Polymer Optoelectronic Device
Polymer Solar Cells Polymer Light-emitting Diodes
Substrate
Organic Semiconductor
DielectricSource Drain
Substrate
Organic Semiconductor
DielectricSource Drain
Polymer Thin Film Transistors
Integrated Optoelectronic Devices Based on Conjugated Polymers
Sirringhaus H., Tessler N., Friend RH, Science 1998
Optoelectronic Polymer Lab,
NTU
substrate
gate dielectricgate
active organic layer
source drain
bottom contact
substrate
gate dielectricgate
active organic layer
source drain
top contact
All Organic Thin Film Transistors (OTFT)
Key Materials for OTFT:(1)Active Organic Layer: Organic Semiconductor(2)Source/drain electrodes: Electrical Conducting Materials (PEDOT:PSS for organic case)(3)Gate Dielectrics: Organic polymers(4) Substrate: Highly thermal stable and transparent polymer, e.g., PET, PSF, etc.
Progress on Flexible Organic Display Devices
Reference: Science, 290, 2123 (2000)) Reference: Synthetic Metals 145, 83-85(2004)
In an active Matrix each pixel contains a light-emitting diodes (LED) driven by a Field-effect transistor (FET). The FET performs signal processing while the LED converts the electrical signal processing into optical output.
Applications of OTFTs
Applications of OTFTs
Flexible TFT arrays enabling technologies for a whole range of applications
Important Performance Parameters
Conduction at the semiconductor dielectric interface
Contacts- injection of charges Electronic and ambient stability Fabrication technology
What’s important?
Requirements
for high performance OTFTs
High Mobility High On/Off Ration Low Threshold Voltage Steep Sub-threshold Slope
13
Polymer Field Effect Transistors
Polymer Semiconductor
Dielectric LayerSubstrate/Gate Electrode
L
W
+ + + + + + + + + + ++
Vg > 0
Vd > 0
-- - - - - - - - - - -
-
Source Drain Printability Flexibility Low cost & weight Easy fabrication
Why Polymer?
Architecture of transistor device
Requirements for high performance
High mobility (>0.1 cm2/VS) High On/Off current Ratio (>104) Low Threshold Voltage (within ±5 V)
Conduction at the semiconductor dielectric interface
Contacts- injection of charges Electronic and ambient stability Fabrication technology
What’s important?
Device Configuration of OTFTs
Operation Energy Diagram and Important Parameters
P type N type
Hole transportElectron transport
Field Effect Mobility (μ)
How strongly the motion of an electron or hole is
influenced by an electric field 2/1
2
L
CW i The Slope of ID1/2-VG @ saturation region
On/Off Current Ratio (Ion/Ioff)
(a) Off : the state of a transistor is then on voltage is applied between the gate and source electrode
(b) On : drain and source current increases due to the increased number of charge carriers
Mobility (a Si-H electron μ ~1cm2/VS)
Ion/Ioff current ratio (diving circuits in LCD Ion/Ioff >106)
Working Principle of OTFTs
VTh Threshold Voltage
Vd Drain Voltage
Vg Gate Voltage
Id Drain Current
L Channel lengthW Channel width
Linear regime
Saturation regime
Start of saturation regime at pinch-off
Current-Voltage (I-V) Characteristics
Transfer (Id-Vg) Curve
Field Effect Mobility (μ) [cm2/VS]
Sub-threshold Slope (SS)
Threshold Voltage (VTh)
On/Off Current Ratio (Ion/Ioff)
2/1
2
L
CWslope i
Performance Parameters
at saturation region
Current-Voltage (I-V) Characteristics
X=0 to L, V(x)= O to Vds
Linear region Vds << Vg Saturation region Vds ~ Vg - VTh
ig
satdssat WC
L
V
I 2)(2
2/1,
Current-Voltage (I-V) CharacteristicsOutput (Id-Vd) Curve
Semiconductor Layer
Materials for OTFTs
Insulator Layer
Electrode
Organic S.C.
Small molecules
(ex: pentacene, oligothiophene)
Conjugated polymers
(ex: P3HT, F8T2) Inorganic S.C. (ex: a-Si, Zinc oxide)
Organic Dielectric
(ex: Polyimide, PMMA, PVP) Inorganic S.C.
(ex: SiO2, TiO2, Al2O3)
Metal (ex: Au, Ca) Conjugated Polymer (ex: PEDOT:PSS)
Materials Requirements of Organic Semiconductors for OTFT
Target: > 1 cm2/Vs on/off ratio >106 for n type or p/n type Organic Semiconductors
Conjugated π-Electron System High Electron Affinity ( for n type) or Ambipolar Characteristics (for p/n type)
Good Intermolecular Electronic Overlap
chemical bonding between molecules, molecular symmetry, the symmetry of the crystal packing….
Good Film Forming Properties
polycrystalline film be highly oriented so that fast transports direction in the grains lie parallel to the dielectric surface
Chemical Purity
charge trapping sites, dopants (increase the conductivity in off state)
Stability
device operation (Threshold Voltage Shift), air stability(O2, H2O)
Requirements of Materials for OTFTs
Factors Influencing The OTFTs Performance
Evolution of The OTFT mobility
for P type or N type Semiconductors
Adv Mater 2002, 14, 4436
mobility (a Si-H μ~1cm2/VS)
P type mobility N type mobility
1-5 ~ 10-3 cm2/VS 1~ 10-5 cm2/VS
Characteristics of Organic Semiconductors
Applications
Light emitting diode, photoconductor, thin film transistor, sensor (PH or gas), solar cell, photovoltaic device…
P type or N type
Charge transport by hole (Low IP) or electron (High EA)
IP
HOMO
LUMO
Vacuum Level
Energy
EA
Bandgap
Acc Chem Res 2001, 34, 359
Heterocyclic Oligomers
Linear Fused Rings
Two dimensional Fused Rings
Polymeric Semiconductors
Structures of P-Channel Semiconductors with TFT Characteristics
Structures of P-Channel Semiconductors with Known TFT Characteristics( Dimitrakopoulos and Malenfant, Adv. Mater.2002)
Mobility in the range of 10-3 ~ 1-5 cm2V-1S-1
mobility (a Si-H μ~1 cm2/Vs)
Single Crystal of High Mobility Organic Semiconductors
Materials Requirements for n-Channel Organic Semiconductors
Conjugated π-Electron System with High Electron Affinity
(EA > 3.0 eV)
Good Intermolecular Electronic Overlap chemical bonding between molecules, molecular symmetry, the symmetry of
the crystal packing….
Good Film Forming Properties
polycrystalline film be highly oriented so that fast transports direction in the grains lie parallel to the dielectric surface
Chemical Purity
charge trapping sites, dopants
Stability
device operation (Threshold Voltage Shift), air stability(O2, H2O)
Chem. Mater. 2004, 16, 4436
Materials issues Materials Design and Preparation (HT%, regioregular, repeating conju
gated unit, substituent, synthesis method, refinement)
Key materials Optimization (gate, source, drain, substrate, dielectric)
TFT Structures Chemical Treatment on dielectric film surface ( silane layer pretreatm
ent, SAMs thiol-based chemical modified contact)
Modifying the TFT structure (bottom contact or top contact)
Processing Optimization Organic layer deposition (i) vacuum evaporation (ii) spin coating, solut
ion casting, printing
Controlling the deposition parameters (aging, deposition rate, anneal process, solvent quality, channel length, channel dimension, deposition thickness, solvent evaporation temperature)
Enhancement on the OTFT Characteristics
Metal-Phthalocyanines
~ 0.6 cm2V-1S-1
Addition of Electron Withdrawing Groups (cyano, perfluoroalkyl) to p Type Cores
10-4 ~ 0.1 cm2V-1S-1
Perylene or Naphthalene Derivatives
10-4 ~ 0.6 cm2V-1S-1
C60
~ 0.3 cm2V-1S-1
Structures of n-Channel Semiconductors with known TFT Characteristics ( C. D. Frisbie and coworkers, Chem. Mater. 2004)
Need to develop polymer semiconductors with high electronic mobility(>1 cm2/Vs)!
10-1 ~ 10-5 cm2/VS
Introduction to PTCDA and PTCDI-R
Optoelectronic Polymer Lab, NTU
Year CompoundMobility (cm2V-1S-
1)Ion/Ioff
1997 PTCDA 10-4~10-5 -
1996 PTCDI 1×10-4 -
2000 PTCDI-C18H37 0.11 -
2002 PTCDI-C8H17 0.6 >105
2004 PTCDI-C5H11 0.05 -
NN
O
OO
O
RRR= CH2C6H4CF3
R= C8H17
Optoelectronic Polymer Lab,
NTU
H.E. Katz et al., Nature 2000, 404, 479
H.E. Katz et al., JACS 2000, 122, 7787
Air stable PTCDI-R or NTCDI-R
NTCDI-CH2C7F15
NTCDI-C8H17
NTCDI-C6H4CF3
Less negative reduction potential of fluorinated chains may be stabilized during operation in air
Denser packing of fluorinated chains could be more permeable to oxygen and water
Introduction to PTCDI-R
Optoelectronic Polymer Lab, NTU
Single-crystal-like packing
π stacking occurs parallel to the substrate surface
Optoelectronic Polymer Lab,
NTU
Why Using PTCDI-R as N Type OTFTs
Single-step synthesis
Impart additional electron withdrawing character to the conjugated backbones to stabilized electron injection.
Provide screening against penetration of environmental contaminants (H2O, O2..)into the channel region.
The side group could induce a more favorable packing geometry that increases intermolecular overlaps or reduces phonon scattering.
PFO
5.7 / 2.4
3X10-4 / 5X10-3
OCC10-PPV
5.0 / 2.8
5X10-4 / 8X10-5
F8BT
5.9 / 3.3
NA / 4X10-3
MEH-PPV
5.0 / 2.8
5X10-5 / 3X10-5
F8T2
5.5 / 3.1
5X10-3 / 6X10-3
CN-PPV
5.4 / 3.2
NA / 4X10-5
PPV
5.2 / 2.7
NA / 1X10-4
P3HT
4.9 / 2.7
2X10-4 / 6X10-4
Mobility for Semiconducting Polymers
RH Friend et al, Nature 2005, 434, 194
HOMO / LUMO (eV) Hole / Electron mobility (cm2V-1S-1)
Ca s-d electrode
CompoundHole/Electron Mobility
(cm2V-1S-1)Ref.
0.004
0.005Science 1995, 269,1560
1.1×10-5
4.3×10-5
J Mater Chem 2004,14, 2840
2.5×10-3
NAChem Mater 2004,16, 4616
3.4×10-4
5.4×10-3
Macromol Rapid Commun. 2005, 26, 1214
10-4
10-5
Chen and Jenekhe (to be submitted to Macromolecule
s)
Comparable Electron & Hole Mobility for OTFT: Donor-Acceptor Systems
NN
O
N
O
Nn
S
NN
C7H15 C7H15
n
38
Donor-Acceptor Conjugated Polymer Semiconductors with High FET Mobility (Literature~2009)
S
S
C12H25
N
NO
O
S
S
C12H25
nS S
C16H33 C16H33 NS
N
n
NC CN
NC CN
S
C12H25
S
C12H25
n
S
C12H25
S
NN
S
C12H25C12H25 C12H25
n
N
N
O O
O O
C10H21
C8H17
C10H21
C8H17
S
S
n
S
S
C14H29N
SS
S
C14H29
nN
S
C14H29
C14H29
0.1 cm2/VS
0.1 cm2/VS
Adv. Mater. 2008, 20, 2217
J. Am. Chem. Soc. 2008, 130, 8580
0.1 cm2/VS0.2 cm2/VS
1.4 cm2/VS
Adv. Mater. 2009, 21, 209
J. Mater. Chem. 2009, 19, 591
0.85 cm2/VS
Nature. 2009, 457, 679
J. Am. Chem. Soc. 2009, 131, 25210.2 cm2/VS
Hole/Electron mobility
Q: Could we develop new solution-processable semiconducting polymers with mobility > 1 cm2/Vs and good environmental stability?
IBM J. Res. and Develop. 2001, 45, 11
Conduction Mechanism in OTFT Channel
Charge carrier mobility is dependenton molecular order within the
semiconducting thin film
Current modulation isachieved by electricfield-induced charge
build-up at theinterface between the
organic semiconductorand the insulator
Charge Transport in Organic Crystal
Limit of mobility in organic single crystal at room temperature is due to the weak intermolecular interaction forces (van der waals interaction) of 10 kcal/mole (cf 76 kcal/mole for Si covalent bond)
Strong π-orbital overlap Band transport Negative temp coefficient
Weak π-orbital overlap Hopping transport Positive temp coefficient
Band transport
Hopping transport
Fi >> Fv Fi ~ Fv
Fi intermolecular interaction force ; Fv thermal vibration force
Charge Transport in Polymer
Intra-Molecular
Soliton Propagation :μ~1000 cm2/VS
Inter-Molecular
Hopping transport :μ~10-2cm2/VS
It is important to increase molecular ordering to obtain high mobility in OTFT devices
Organic & Inorganic Semiconductors
Organic Semiconductor Inorganic Semiconductor
Weak Van der Waals interaction forces π-bond overlapping Molecular gas property (molecule’s identit
y) Hopping type charge transport dominant Low mobility and small mean free path
Strong covalent bonds ρ-bond Only crystal property Band type charge transport d
ominant High mobility and large mean
free path
Bipolar OTFT- Organic Semiconductors in Interfacial Properties
Idealized energy level diagram of OTFTs P- & N- Channel OTFT Operation
Scattering Mechanism in Thin Film
Flat & clean surface Large grain No doping
For high mobility
Operation Energy Diagram and Important Parameters
P type N type
Hole transportElectron transport
Field Effect Mobility (μ)
How strongly the motion of an electron or hole is
influenced by an electric field 2/1
2
L
CW i The Slope of ID1/2-VG @ saturation region
On/Off Current Ratio (Ion/Ioff)
(a) Off : the state of a transistor is then on voltage is applied between the gate and source electrode
(b) On : drain and source current increases due to the increased number of charge carriers
Mobility (a Si-H electron μ ~1cm2/VS)
Ion/Ioff current ratio (diving circuits in LCD Ion/Ioff >106)
Chemical surface treatment on dielectric film surface or electrode
(SAMs silane layer pretreatment, plasma treatment)
Modify the TFT structure
(bottom contact or top contact)
Control the processing parameters
(deposition rate, anneal process, solvent power, channel dimension, deposition thickness, heat treatment, film forming method)
Choose materials
(gate, source, drain, substrate, dielectric)
Organic P3HT selection
(HT% regioregularity, molecular weight, substituent, synthesis method, refinement)
Enhancement on Performance of OTFTs
Surface treatment on Inorganic Dielectric
Hexamethyldisilazene (HMDS) Octadecyltrichlorosilane (HMDS) Other silanes Alkanephosphonic acid
Self-Assembly Monolayer (SAM)
Increased grain boundary of OSC Hydrophilic to hydrophobic
attachment (smooth surface)
Increasing molecular ordering Obtain improved OTFT characteristics
Adv. Funct. Mater. 2005, 15, 77
Self-Assembly Monolayer (SAM)
Surface Treatment on Inorganic Dielectric
Chemical Treatment on Dielectric Surface
Synth Met. 2003, 139, 377
Plasma pretreatment
untreatment
Un-treatment
Plasma treatment
Plasma treatment
RMS roughness:
0.8 ~ 1.3 nm
RMS roughness:
0.3 ~ 0.5 nm
Higher mobility after plasma treatment
DielectricsRequirements for OTFT Dielectrics
High dielectric constant for low-voltage operating Good heat and chemical resistance Pinhole free thin film formability with high breakdown voltage and
long term stability Comparable with organic semiconductor in interfacial properties
Polymeric Dielectrics
Adv. Mater. 2005, 17, 1705
The conduction mechanism in organic semiconductor is different from that of inorganic.
Due to the weak intermolecular forces in OSC, the number of effects through which the dielectric can influence carrier transport and mobility is much broader than in inorganic materials.
Morphology of organic semiconductor and orientation of molecular segments via their interaction with the dielectric (especially in bottom gate devices)
Interface roughness and sharpness may be influenced the dielectric itself, the deposition conditions, and the solvent used
Gate voltage dependent mobility, which together with the variation of the threshold voltages, can be a signature of dielectric interface effects
The polarity of dielectric interface may also play a role, as it can affect local morphology or the distribution of electronic states in OSC.
Dielectric Effect in OTFTs
Dielectrics
Inorganic Insulator for OTFTs
Surface states on inorganic oxides are particular problem leading to interface trapping and hysteresis, also impacts the semiconductor morphology
Large number of surface treatment studies!
Dielectrics
Organic Insulator for OTFTs
Organic dielectrics offers the freedom to build both top and bottom gate devices more easily by the use of solution coating technique and printing
Dielectrics
Why high K insulators have better OTFT performances?
For parallel plate capacitor filled with dielectrics
d
AkC o
The mobility depends on the concentration of carriers accumulated in
the channel in the OTFTs, the insulators should be thinner and its dielectric
constant should be higher to induce a larger number of carriers at a lower
voltage.
Optoelectronic Polymer Lab, NTU
High K gate dielectric is the expansion of design space due to the possibility
of using thicker gate length.
29.3 SiOdk
d
Optoelectronic Polymer Lab,
NTU
K value
Ta2O5: 25-40
TiO2: 40-80
Si3N4 : 7.5
Al2O3 : 10
Optoelectronic Polymer Lab,
NTU
Threshold Voltage (Vt)
OX
MStt C
QVV '
FSAOX
Ft qNC
V 41
2'
i
AF n
N
q
kTln
FSAOX
Ft qNC
V 41
2'
i
DF n
N
q
kTln
P type N type
The x-axis intercept of ID1/2-VG
d
AkC o
29.3 SiOdk
d
d k c Vt
but high leakage current (high off current) !!
Smooth interface between the polymer-semiconductor and dielectric to reduced scattering at the smooth interface
Use High k Materials as Gate Dielectrics
IEEE Trans. Electron Devices. 2001, 14, 281
Why choosing Organic materials as insulators?
The drawbacks of using inorganic materials as insulators: Difficulty on building electronic devices on plastic substrate; High processing temperature、 adhesion to substrate、
processing method、 Cost、 large area?
Year Organic
active layer
Dielectrics Substrate Mobility
(cm2/VS)
Fabrication
1994 DH6T Polyester(3) PET 0.06 spin coating
1997 P3HT Polyimide Polyester 0.03 spin coating
1998 P3HT Polyimide PET 0.05 Screen printing
1999 PTV PVP polyimide 3×10-4
2000 F8T2 PVP 0.02 spin coating
2001 Pentacene… Organosilsesquioxane
PET 0.1 spin coating
2002 Pentacene
P3HT
P4VP(4.2) Glass 0.05 spin coating
2002 Pentacene… Organosilsesquioxane
ITO/Mylar 0.1 spin coating
2002 Pentacene PVP glass
PEN
0.3
0.05
spin coating
2003 Pentacene PVP PEN 0.7 spin coating
2003 pentacene PVA(3) glass 0.01 spin coating
2003 pentacene JSS-362 PET 0.12 spin coating
2003 pentacene Al2O3 /JSS-362
(2.2-1.7)
PEN 1.4×10-2 Sputtering
/Spin coating
Optoelectronic Polymer Lab,
NTU
Al2O3 /JSS-362 as dielectric double layers
Low dielectric constant of organic materials : reducing leakage current
Inorganic materials : supply the adhesion force between the dielectric layer and S and D electrode
Synth. Met. 2003, 139, 445
Contact Electrode Requirement for S/D Electrodes
No interface barrier with the active layer No metal diffusivity High carrier injection, low contact resistance
Au
Mainly used as S/D electrodes due to its high work function (5.1 eV) and low injection barrier
Still remain dipole barrier
Contact Electrode
Environment StabilityOff current increase by oxygen doping process
Chemical surface treatment on dielectric film surface or electrode
(SAMs silane layer pretreatment, plasma treatment)
Modify the TFT structure
(bottom contact or top contact)
Control the processing parameters
(deposition rate, anneal process, solvent power, channel dimension, deposition thickness, heat treatment, film forming method)
Choose materials
(gate, source, drain, substrate, dielectric)
Organic P3HT selection
(HT% regioregularity, molecular weight, substituent, synthesis method, refinement)
Improvement of P3HT OTFTs
Control the Processing ParametersSolvent Power
Appl Phys Lett, 1996, 69, 4108
P3HT in chloroform
P3HT in TCB
Less crystalline
Nanoribbons ~μm
Lamellar layer
structure
π - π interchain stacking
Chem Mater 2004, 23, 4775
Mobility increase with higher bp of solvent
Control the Processing ParametersSolvent Power
Control the Processing ParametersAnnealing
Alignment
Molecular weight
Organic P3HT Selection
Adv Mater, 2003, 15, 1519
Adv. Funct. Mater. 2004, 14, 757
Organic P3HT Selection
Macromolecules 2005, 38, 3312
High Mw P3HT
Low Mw P3HT
Chare carriers trapped on the nanorod
Interconnect ordered area and soften the boundary
Molecular Weight
Mobility increase with higher MW
Organic P3HT Selection
HT% regioregularity
Nature, 1999, 401, 685
Synth Met. 2000, 111-112, 129
Organic Compound SelectionAlkyl chain length
Synth Met. 2005, 148, 169
Chemical Treatment on Dielectric Surface
Synth Met, 2003, 139, 377
Plasma pretreatment
untreatment
Un-treatment
Plasma treatment
Plasma treatment
RMS roughness:
0.8 ~ 1.3 nm
RMS roughness:
0.3 ~ 0.5 nm
Higher mobility after plasma treatment
Semiconductor Deposition Methods
Organic semiconductors are deposited either from vapor or solution phase depending on their vapor pressure and solubility
Device performance of OTFTs is greatly influenced by various deposition conditions due to the different resulting molecular structure and thin film morphology
How to Get High Mobility ?
Homo/LUMO of the individual molecules must be at levels where hole/electrons can be induced at accessible applied electric fields.
The solid should be extremely pure since impurities act as charge carrier traps.
The molecules should be preferentially oriented with the long axes approximately parallel to the substrate since most efficient charge transport occurs along the direction of intermolecular π-πstacking
The crystalline domains of the semiconductor must cover the area between the S and D contacts uniformly.
Ways of Mobility Improvement
G. Horowitz, Adv. Mater. 2000, 14, 365
Katz, H. E.; Bao, Z., J. Phys. Chem. B., 2000, 104, 671
Dimitrakopoulous, C. D.; Mascaro, D. J., IBM J. Res. & Dev. 2001, 45,11
Katz, H. E.; Bao, Z.; Gilat, S. L., Acc. Chem. Res., 2001, 34, 359
Dimitrakopoulous, C. D.; Malenfant, D. R. L. Adv. Mater. 2002, 14, 99
Horowitz, G. J. Mater. Res. 2004, 19, 1946
Newman, C. R.; Frisbie, C. D.; da silva Filho, D. A.; Bredas, J. L.; P. C. Ewbank, Mann K. R. Chem. Mater. 2004, 16, 4436
Veres, J.; Ogier, S.; Lloyd, G. Chem. Mater. 2004, 16, 4543
Ling, M. M.; Bao, Z. Chem. Mater. 2004, 16, 4824
Chua, L. L.; Zaumsell, J.; Chang, J. F.; Ou, E. C. W.; Ho, P. K. H.; Sirringhaus, H.; Friend, R. H. Nature, 2005, 434, 194
Sun, Y.; Liu, Y.; Zhu, D. J. Mater. Chem. 2005, 15, 53
Facchetti, A.; Yon, M. H.; Marks, T. J. Adv. Mater. 2005, 17, 1705
Sirringhaus, H. Adv. Mater. 2005, 17, 2411
Reichmanis, E.; Katz, H. E.; Kloc, C.; Maliakal, A. Bell Labs Technical J. 2005, 10, 87
Dodabalapur, A. Materials Today 2006, 9 , 24
Facchetti, A. Materials Today 2007, 10, 28
Zaumseil, J.; Sirringhaus, H. Chem. Rev. 2007, 107, 1296
Reference
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