Here is a copy of Professor Janos Veres, Chief Technical Office at Polyphotonix, seminar which was presented in our studio in London. From zinc oxide and non-toxic nanocrystals to the super material grapheme Prof. Veres looked at current and potential directions for lighting technology and examine the implications for the way we use and design with light in the future

1. Light Sources of the Future –
OLED and beyond
Janos Veres, CTO, janos@polyphotonix.com
www.polyphotonix.com

2. 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 ?

3. 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

4. Light
Light 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

5. 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
Emission spectrum
Krypton
Mercury
Neon
Water vapour
Absorption spectrum Xenon

6. Energy and excitation levels: solids
Solids: atoms interact, energy levels start splitting, discrete levels become “energy bands”
Discreet lines are more difficult to observe

7. Incandescence and blackbody radiation
Emission of light from a hot Radiation of a blackbody
body due to its temperature
The “Planckian Locus” in a colour space The sensitivity of the eye

8. Sunlight
Solar radiation spectrum
Radiation of a blackbody

9. From incandescence to exciting gases and solids
Incandescence Thermionic emission
Emission of light from a hot Heat induced flow of charge
body due to its temperature from a surface.
Cathodoluminescence
Beam of electrons excites a
luminescent phosphor
(television)
Charge:
Fluorescent sources
Electrons (thermionic) emitted ionise a gas.
The relaxation of gas molecules emit UV light.
UV is in turn used to excite a phosphor.

10. 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

11. 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

12. OLED
Certain organic materials are semiconductors!
Photoluminescence+ electronic transport=electroluminescence
Light Emitting Diodes can be built that resemble LED
Visible light
Low workfunction
cathode hυ
Ca, Li, Al etc. + + + + + +
+
- - -
LUMO + +
+
3–6 V
- -+ + +
-
+
- -
+ + -
HOMO
High workfunction - - - - - -
Anode
Au, ITO, Pt etc.

13. 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
O O Polythienylene-
R R' Vinylene (PTV)
R N N R
O n
O
S N
perylenes
R polyfluorenes
O N O
R R Pentacene X
N
X
S R
Oligo, poly- PPVs
O N O -thiophenes n
Y
R n
PTAA
NTDI derivatives R'
e-
e-
LUMO LUMO
LUMO: orbitals overlap
ambipolar
h+ p-type
n-type h+
HOMO
HOMO
Adopted from J. Veres, MRS Spring 2006 HOMO: orbitals overlap

14. Organics are disordered
Molecular orientation, surrounding of molecules influences them
Extended state
May be a molecule, chain segment or domain
e-
LUMO 1. molecular energies vary
due to local orientation & polarisation effects
n-type Low dipole moment, symmetry
Reduce impurities
HOMO
3. Orbital size and shape Transition probability
4. Charge in orbitals p = n exp(–2R/r – DE/kT)
e-
DEh
2. molecular relaxation introduces further
energy difference
Larger molecules (i.e. extended states) help
Adopted from J. Veres, MRS Spring 2006

15. Evaporated OLED
Multilayer structures for dedicated tasks
Electrode mathcing, emission colour, carrier confinement
Low work function metal
Cathode
ETL (Electron Transport layer) Alq3
HBL (hole blocking layer)
Host:Dopant Various dyes
HTL 2 (Hole Transport Layer)
HTL 1 Triarylamines
HIL (Hole Injection Layer)
Anode ITO Copper-Phthalocyanine /
Glass PEDOT PANI

16. Excited states in organic LEDs
p-
p+
recombination
↑↑
1
( ↑↓ + ↓↑ )
1
2
( ↑↓ − ↓↑ ) singlet exciton triplet exciton 2
↓↓
radiative non-radiative non-radiative decay
decay decay
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

18. Source: Universal Display OLED review

19. Source: Universal Display OLED review

20. 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)

21. Quantum confinement
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
ZnO
TiO2
4
ZnO TiO2
Eg (eV)
4
Eg (eV)
3 3
400 400
λonset (nm)
λonset (nm)
350 350
300 300
250 250
0 5 10 0 5 10
d (nm) d (nm)
Source: J. Galloway, Johns Hopkins univ. 2007

22. 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

23. QD fabrication
Epitaxy, patterned growth
E-beam lithography
Etch pillars in quantum well heterostructures
1D vertical confinement due to mismatch of Growth on patterned substrates
bandgaps (potential energy well) Grow QDs in pyramid-shaped recesses
Pillars provide confinement in the other 2 Recesses formed by selective ion
dimensions etching
Disadvantages: Slow, low density, defects Disadvantage: density of QDs limited
by mask pattern
A.Scherer and H.G. Craighead. T. Fukui et al.
Appl. Phys. Lett., Nov 1986. Appl. Phys. Lett. May, 1991

24. QD fabrication
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
P. Petroff, A. Lorke, and A. Imamoglu. Physics Today, May 2001.

25. QD fabrication
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”)
C. B. Murray, et al Annual Rev. Mater. Sci. 30, 545, 2000.

26. 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

27. Quantum dots for white LED
Evident, QD Vision, Nanoco

28. 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

29. QD for biology & sensing
Source: Justin Galloway, Johns Hopkins

30. 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. Towards LED and OLED
Today Tomorrow
?
inefficient environmental impact LED: efficient spot light OLED: efficient area light
LED and OLED will dominate
31

32. LED growth
Strong growth despite high prices and recession in 2008-2009
Source: Strategies Unlimited)

33. 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
34

35. Real energy efficiency depends on the luminaire!
OLED has the opportunity to be the luminaire itself
LED
Incandescent
CFL
Picture or graphic here
Source: DOE Round 9 CALiPER Report

36. 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

37. OLED lighting today
Source: DisplaySearch

38. OLED lighting today – commercial devices

39. OLED lighting today -demos
Source: Philips, GE, Add-Vision, Osram

40. Long term vision
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
Source: Osram, Konica Minolta, Acuity Brands 40

41. The Printed Electronics industry will eventually become
as big as the semiconductor industry
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
It creates new possibilities for business, new business's and wealth creation.
The step Printed Electronics from integrated circuits is as equally
important as that from vacuum tubes to transistors

42. 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

43. The Importance of Design
Richard Kirk, Founder of PolyPhotonix has a recognised background creating markets in the
field of Printed Electronics
Jonas 2006
Animated Wallpaper

44. It’s not just the Science…..
Working with artists via the creation
of an art foundation

45. Printed Electronics in Architecture
Alcatel Boardroom, Paris, France Radisson Stanstead Wine Tower, UK

46. Heathrow Terminal 5
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
Troika, London

47. Advertising
Experience with every outdoor company in Europe and North America
Delivery and installation
Integrated solutions
Examples of outdoor installations in Paris.

48. Fashion
The HSBC Advert was shown in 180 countries Gareth Pugh 2007

49. 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

50. The UK Printable Electronics Centre
PETEC
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

51. 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.

52. 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

53. 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

54. 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

55. Summary
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!