OLeds and Beyond- Light Sources of the Future Seminar
-
Upload
fagerhult-lighting -
Category
Technology
-
view
1.852 -
download
3
Transcript of OLeds and Beyond- Light Sources of the Future Seminar
Light Sources of the Future –
OLED and beyond
Janos Veres, CTO, [email protected]
www.polyphotonix.com
Agenda
Light
How to turn electricity into light ?
The solid state lighting revolution
The next wave: LED and OLED
New materials on the horizon
Radical concepts
Where is the lighting industry moving ?
PolyPhotonix
Innovative SME based in the North East of England within PETEC (The UK National Centre for
Printed Electronics).
Established in early 2009
Focus on the application end of OLED technology - disruptive, radical uses in:
Architectural lighting, medical devices and automotive lighting/ambient interiors
LightLight is electromagnetic radiation: waves and particles at the same time
Produced by exciting a substance with a variety of means
(heat, light, charged particles, chemical or biological)
Excitation and subsequent emission corresponds to transfer of energy between discrete levels
in matter
Energy and excitation levels: gases
Sharp, discrete energy levels for individual atoms/molecules
Electrons transitioning between levels produce distinct absorption/radiation colours
Bromine
Deuterium
Helium
Hydrogen
Krypton
Mercury
Neon
Water vapour
Xenon
Emission spectrum
Absorption spectrum
Energy and excitation levels: solids
Solids: atoms interact, energy levels start splitting, discrete levels become “energy bands”
Discreet lines are more difficult to observe
Incandescence and blackbody radiation
Emission of light from a hot
body due to its temperature
The sensitivity of the eyeThe “Planckian Locus” in a colour space
Radiation of a blackbody
Sunlight
Radiation of a blackbody
Solar radiation spectrum
From incandescence to exciting gases and solids
CathodoluminescenceBeam of electrons excites a
luminescent phosphor
(television)
IncandescenceEmission of light from a hot
body due to its temperature
Thermionic emissionHeat induced flow of charge
from a surface.
Charge:
Fluorescent sourcesElectrons (thermionic) emitted ionise a gas.
The relaxation of gas molecules emit UV light.
UV is in turn used to excite a phosphor.
Electroluminescence: LEDs
First practical visible device 1962 red
(Holonyak, GE)
p and n type layers deliver holes and
electrons to a recombination zone
Emission colour is determined by
bandgap of active layer
From Kazarinov and Pinto,
IEEE J. Quantum El.
30, 49, 1994
White LEDs
Emission is centered around a single peak: bandgap
White is achieved either by phosphors or RGB devices combined
High colour rendering is a challenge
See http://en.wikipedia.org/wiki/Light-emitting_diode
3–6 V
-
+
+
--
+
- - - - - -
+ + + + + +
-
+
- +- +
Visible light
OLED
Certain organic materials are semiconductors!
Photoluminescence+ electronic transport=electroluminescence
Light Emitting Diodes can be built that resemble LED
HOMO
LUMO
hυ
High workfunction
Anode
Au, ITO, Pt etc.
Low workfunction
cathode
Ca, Li, Al etc.+
+ +
- - -
+
Organic semiconductors• Molecular solids. Intrinsic semiconductors
• Localisation is strong (especially in amorphous materials)
• bias for n or p type character due to electron donating/withdrawing groups
N
N
OO
OO
R
R
NTDI derivatives
S N
Polythienylene-
Vinylene (PTV)N N RR
O
OO
O
perylenes
PentaceneS
R R
Oligo, poly-
-thiophenes
polyfluorenes
LUMO: orbitals overlap
HOMO
e-
n-type
N
n
X X
Y
PTAA
R'R
n
R'
R
n
PPVs
HOMO
LUMO
h+
ambipolar
e-
HOMO: orbitals overlap
LUMO
h+p-type
Adopted from J. Veres, MRS Spring 2006
HOMO
Organics are disorderedMolecular orientation, surrounding of molecules influences them
1. molecular energies vary
due to local orientation & polarisation effectsLow dipole moment, symmetry
Reduce impurities
Transition probability
p = n exp(–2R/r – DE/kT)
Extended state
May be a molecule, chain segment or domaine-
n-type
LUMO
DEh
2. molecular relaxation introduces further
energy differenceLarger molecules (i.e. extended states) help
e-
3. Orbital size and shape
4. Charge in orbitals
Adopted from J. Veres, MRS Spring 2006
Cathode
ETL (Electron Transport layer)
HBL (hole blocking layer)
Host:Dopant
HTL 2 (Hole Transport Layer)
HTL 1
HIL (Hole Injection Layer)
Anode ITO
Glass
Low work function metal
Alq3
Various dyes
Triarylamines
Copper-Phthalocyanine /
PEDOT PANI
Evaporated OLEDMultilayer structures for dedicated tasks
Electrode mathcing, emission colour, carrier confinement
triplet excitonsinglet exciton
p+
recombination
radiative
decay
radiative
decay
non-radiative decaynon-radiative decaynon-radiative
decay
non-radiative
decay
(((( ))))↓↑↓↑↓↑↓↑−−−−↑↓↑↓↑↓↑↓2
1 (((( ))))↓↑↓↑↓↑↓↑++++↑↓↑↓↑↓↑↓2
1
↑↑↑↑↑↑↑↑
↓↓↓↓↓↓↓↓
p-
Excited stated decay following spin statistics:
singlet: triplet ratio is 1:3, allowing only 25% efficiency by luminescence
Phosphorescence:
Certain metal complexes allow radiative emission from triplet states
Excited states in organic LEDs
Source: Universal Display OLED review
Source: Universal Display OLED review
Quantum dots
Semiconductor nanoparticles that exhibit quantum confinement (typically <10nm)
Nanoparticle: inorganic material (e.g. CdSe) with a diameter less than 1nm
Properties are tuned by the size of crystalline dots
Can be functionalised
Source: Evident Technologies & AIST Today Vol.6, No 6 (2006)
Quantum confinement
ZnO
3
4
Eg (
eV
)
250
300
350
400
λo
nse
t (n
m)
0 5 10
d (nm)
ZnO
3
4
Eg (
eV
)
250
300
350
400
λonset
(nm
)
0 5 10
d (nm)
TiO2
TiO2
ZnO has small effective masses and quantum effects can be observed for particle sizes <8nm
TiO2 has large effective masses thus quantum effects are difficult to observe
Source: J. Galloway, Johns Hopkins univ. 2007
Surface functionalisation
Surface states need to be terminated
Particles need to be separated to stop interacting
Inorganic shell grown
Polymeric functionalisation- solubility, dispersibility!
Specific binding sites: sensing/medical applications
Voura, E. B., Jaiswal, J. K., Mattoussi, H. & Simon, S. M. Nature Med.
2004(10), 993–998 Source: Evident Technologies
QD fabrication
E-beam lithography
Etch pillars in quantum well heterostructures
1D vertical confinement due to mismatch of
bandgaps (potential energy well)
Pillars provide confinement in the other 2
dimensions
Disadvantages: Slow, low density, defects
Growth on patterned substrates
Grow QDs in pyramid-shaped recesses
Recesses formed by selective ion
etching
Disadvantage: density of QDs limited
by mask pattern
Epitaxy, patterned growth
A.Scherer and H.G. Craighead.
Appl. Phys. Lett., Nov 1986.
T. Fukui et al.
Appl. Phys. Lett. May, 1991
Self-organized QDs through epitaxial growth strains
Stranski-Krastanov growth mode (use MBE, MOCVD)
Islands formed on wetting layer due to lattice mismatch (size ~10s nm)
Disadvantage: size and shape fluctuations, ordering
Control island initiation
Induce local strain, grow on dislocation, vary growth conditions, combine with patterning
QD fabrication
P. Petroff, A. Lorke, and A. Imamoglu. Physics Today, May 2001.
Reactions engineered to precipitate quantum dots from solutions or a host material (e.g. polymer)
Surface is capped so the dot remains chemically stable
Can form “core-shell” structures, by sequential growth
Typically group II-VI materials (e.g. CdS, CdSe)
Disadvantage: Size variations ( “size dispersion”)
QD fabrication
C. B. Murray, et al Annual Rev. Mater. Sci. 30, 545, 2000.
Quantum dots - properties
High quantum yield
Narrower and more symmetric emission spectra
100-1000 times more stable to photobleaching than organics
High resistance to photo-/chemical degradation
Tunable wave length range 400-4000 nm CdTe
J. Am. Chem. Soc. 2001, 123, 183-184
Quantum dots for white LED
Evident, QD Vision, Nanoco
Quantum dot electroluminescent devices
The next step in solid state devices!
Direct injection of holes and electrons into the quantum dots
Challenges: surface states on dots
Balancing carrier transport and isolation of quantum dots for their optical properties
Potentially coatable, printable like OLED !
J.M. Caruge et al, Nature Photonics, 2, 247, 2008
QD for biology & sensing
Source: Justin Galloway, Johns Hopkins
Lighting today
Lighting is a $90B industry and growing
rapidly
2/3 of all artificial light is generated by
fluorescent area lights
Quality of light, glare, efficacy, and toxic
mercury are fluorescent’s shortcomings
31
Tomorrow
LED and OLED will dominate
inefficient environmental impact
Today
LED: efficient spot light OLED: efficient area light
?
Towards LED and OLED
LED growth
Strong growth despite high prices and recession in 2008-2009
Source: Strategies Unlimited)
The Haitz Law
1) Luminous flux per package increases 30 times each decade
2) Cost per lumen decreases by a factor of 10 each decade.
Source: Roland Haitz, Hewlett-Packard Labs, 1998
34
OLED is real: displays and lighting
Displays
Lihgting
Picture or graphic here
Incandescent
CFL
LED
Source: DOE Round 9 CALiPER Report
Real energy efficiency depends on the luminaire!
OLED has the opportunity to be the luminaire itself
LED and OLED development expectations –DOE roadmaps
Both are predicted to offer important solutions to energy efficiency in the next 10 years
Both can achieve similar power efficiencies.
OLED is approximately 3 years behind LED
Source: DOE Roadmaps
OLED lighting today
Source: DisplaySearch
OLED lighting today – commercial devices
OLED lighting today -demos
Source: Philips, GE, Add-Vision, Osram
40
Inherently large area and low glare light source
Potentially ½ the power consumption of fluorescent
Warm, pleasing color
Green technology – no mercury
Innovative form factors in the future
Long term vision
Source: Osram, Konica Minolta, Acuity Brands
It involves the printing of materials to create electronics.
• It can be very large areas Outdoor Billboards
• It can offer new forms Flexible, Rollable and invisible
• It can be cheaper Low cost materials and manufacturing compared to
conventional electronics
• It can offer improved performance over conventional electronics
The Printed Electronics industry will eventually become
as big as the semiconductor industry
The step Printed Electronics from integrated circuits is as equally
important as that from vacuum tubes to transistors
It creates new possibilities for business, new business's and wealth creation.
Printed, felxible light –
organic or inorganic
• Highly efficient operation
• High quality white light (and/or better colours)
• Long lifetimes
• Thin, flat, large area ‘lambertian’ light source – architects love the idea
• Low voltage, DC driven
• ‘Printable’ – sheet or ‘roll to roll’
• Resistant to shock and vibration
• Multitude of applications
• Conformable and flexible, ability to integrate into architecture
OLED automotive applications
The Importance of Design
Animated WallpaperJonas 2006
Richard Kirk, Founder of PolyPhotonix has a recognised background creating markets in the
field of Printed Electronics
It’s not just the Science…..
Working with artists via the creation
of an art foundation
Printed Electronics in Architecture
Radisson Stanstead Wine Tower, UKAlcatel Boardroom, Paris, France
British Airways, First Class Lounge
10,500 circuits
25 meters x 2.5 meters
All circuits individually addressable
Created by artists that Elumin8 sponsored in the past
Manufacture, design and install, 1/10th of the cost of an equivalent LED wall
Heathrow Terminal 5
Troika, London
Experience with every outdoor company in Europe and North America
Delivery and installation
Integrated solutions
Examples of outdoor installations in Paris.
Advertising
Gareth Pugh 2007The HSBC Advert was shown in 180 countries
Fashion
Printed Electronics in Automotive
Pioneered the use of printed Electroluminescence in transport applications with:
Jaguar, Bentley, Rolls Royce, BAE, Lotus, Aston Martin, Ford, Ascari, JCB,
MOD, Nascar, Toyota, Westland, Nissan among others.
Jaguar CXF
2x 8,000 sq ft clean rooms.
Pilot line processes developed for
•Organic Thin Film Transistors (OTFT);
•Organic Photovoltaic's (OPV);
•Solid State Lighting (SSL)
state of the art equipment set and
world class industry expertise
The UK Printable Electronics Centre
PETEC
PolyPhotonix technology development
• Synergies with technology base for other projects at PETEC
• Secured significant grants for funded projects, over £2 M
• Working with technology providers to source, license existing materials/processes
• Building a development process line
• Exploring proprietary process technologies for follow up phase
• PolyPhotonix is aiming to be one of the first to market with an OLED product.
What does the futurte hold ? Future concepts
Wireless lighting – Tesla experiments
Colour tuning in a single layer
Transparent devices
Photovoltaics and lighting combined
Lighting elements integral part of building elements
Strechable LED arrays
Small LED “chiplets” connected with a wave-shaped wire mesh
Embedded in silicone plastic
Applications: surgical gloves, strechable displays
Source: Kim et al, Nature materials, 9, 929, 2010
Lighting with trees ?
Implanting gold nanoparticles into the leaves of the Bacopa Caroliniana plants.
Under UV excitation, Au nanoparticles produce a blue-violet fluorescence to trigger a
red emission in the surrounding chlorophyll.
Source: Prof Shi-Hiu Chang, Taiwan
Solid state lighting is undergoing a revolution
LED and OLED are both taking off fast
Initially high prices require targeting unique applications
There is plenty of opportunity to innovate:
LED/OLED developments with quantum dots will be significant!
Summary