Organic Light Emitting Diodes: Display and Lighting Technology of the Future

Karl LeoInstitut fr Angewandte Photophysik, TU Dresden, and Fraunhofer-Institute fr Photonische Mikrosysteme, Dresden

Motivation: What is possible with OLED:

Samsung 40 TV display

Organic Semiconductors

Photovoltaic cellsOrganic materials Integrated circuits

Large area & flexible substrates possible

Large variety of materials

Low cost

Small-Molecules

Organic semiconductors: Two variants

Polymers

Technology: Spin-On Technology: Evaporation

pzpz

sp2 sp2

p lane of thesp 2-orb ita ls

pz-orb ita l -bond

-bond

-bond

pz-orb ita l

The basics of organic semiconductors:Conjugated -electron systems

Sp2-hybridised Carbon:

de loka lis ie rte E lektronen

pz

sp2

6 x

18 x

LUMO (*) => EC conduction band

HOMO () => EV valence band

-electron systems delocalize!

VdW crystals small -overlap, narrow bands saturated electron system

delocalized-electrons

Molecules with conjugated -electron system

Technology: vapor deposition

Device energy diagram

E

x

Cathode

LUMO

HOMO

Anode

Device structure

V

A

Light emission

Organic Light Emitting Diodes

OLEDs: Basic Principles

Glass substrate

Transparent anode

Emissive layer

Cathode

++ +

---300nm

Organics Collaboration Dresden

Institut frAngewandte Photophysik

IAPP, University of Dresden (www.iapp.de, approx. 40 people)

Basic research on novel device concepts

Low-voltage OLED

Fraunhofer-IPMS Dresden (www.ipms.fraunhofer.de, approx. 25 people)

Process development with highly efficient OLEDs

OLED-Inline-deposition set-up (30x40cm Substrate)

Driving Electronic for OLED-Displays

Small to medium volume fabrication

Novaled GmbH (www.novaled.com, approx. 45 people)

Highly efficient OLED-stacks for RGB-Displays

Technology licensing

Exponential current-voltage relation

Flat-band under operation

Low work-function contacts not needed !

p n

Why doped transport layers:Inorganic vs. Organic LED

Inorganic LED (e.g., GaAs/AlGaAs) Organic LED

CB

VB

EFe

EFh

Metal

space charge limited currents

low work function metals neededITO-preparation necessary

HTLETL

Double emission layer (D-EML) structure

D-EML structure

Al

BPhen:Cs

BPhen

TAZ:Ir(ppy)3

TCTA:Ir(ppy)3Spiro-TAD

MeO-TPD:F4-TCNQ

ITO substrate

n-doped ETL

HBL

PET-EML

PHT-EML

EBL

p-doped HTL

p-H

TL

EB

L

HB

L

EM

L2

ITO

Al

n-E

TL

EM

L1

Self-balancing EML system no charge accumulation at interfaces

X. Zhou et al., Appl. Phys. Lett. 81, 4070 (2002)

2.6 2.8 3.0 3.210

100

1,000

10,000

Lum

inan

ce (c

d/m

2 )

Voltage (V)

1,000 cd/m2 @ 2.9V61.5 cd/A; 67 lm/W

100 cd/m2 @ 2.68V64 cd/A; 75 lm/W

Highly efficient & stable PIN Triplet OLED:World record in efficiency

G. He et al., Appl. Phys. Lett. 85, 3911 (2004)

Highly efficient devices are also most stable devices

Efficiency higher than for best green nitride LED

Lifetime of PIN-OLEDs

OLEDAsia Seoul 2005

Current status:phosphorescent red (0.68, 0.32):100,000 h at 500 cd/mphosphorescent green (0.38, 0.59): 25,000h at 500 cd/m (Irppy3 based)fluorescent blue (0.15, 0.17): 6,000 h at 500 cd/m

Novaled pin-OLEDs have reached state of the art lifetimes for emitter systems in all three colors samples still contain Cs as n-dopant

100 1.000 10.000

1.000

10.000

100.000

1.000.000

Life

time

/ h

Luminance / cd/m2

200,000 h @ 150 cd/m2

30,000 h @ 500 cd/m2

8,000 h @ 1000 cd/m2

n = 1.7

Red triplet pin OLED

OLEDFAB Project

OLEDFAB Projekt iniated by Thomson und BMWA/SMWA

Novaled leads Saxonian consortium with IPMS und IAPP

Goals: - Demo of a 5 inch active-matrive display with highly efficient pin technology- Display manufactured using novel inline technology

Other partners: - Applied Films - Labor fr Bildschirmtechnik Stuttgart- Deutsche Thomson Brandt

Full color AM display based on pin technology

Performance:

operating voltage for 100cd/m2: around 7V (OLED + backplane)

power consumption:240mW@100cd/m2 (in forwarddirection only, video mode)

about 60% of equivalent LCD display

Active matrix OLED made in joint project by ITRI (Taiwan), Thomson (France) and Novaled

Panel emitting in both directions on n-channel LTPS backplane (3.25, QVGA, 130dpi) based on PIN structure

OLEDFAB: Display with improved backplane in preparation

Even higher Light Efficiencies: out-coupling enhancement

OLEDAsia Seoul 2005

Efficiency at 1000 cd/m: 110 lm/W (with outcoupling enhancement)

Novaled focuses on furtherimprovement of their recordbreaking efficiencies byout-coupling enhancements(target 2005: 140lm/W)

10 100 1000 100000

20

40

60

80

100

120

Pow

er e

ffici

ency

(lm

/W)

Luminance (cd/m)

Green phosphorescent PIN OLEDwith outcoupling enhancement

Institut fr Angewandte PhotophysikTechnische Universitt Dresden

LED performance vs. time

1965 1970 1975 1980 1985 1990 1995 2000 2005

0

20

40

60

80

100

120

0

20

40

60

80

100

120

OLED white Red Filtered

Tungsten Bulb (unfiltered)

Fluorescent Lamp

InGaNgreen

OLED

PLED

AlInGaP Red/Yellow

Pow

er E

ffici

ency

(Lum

en/W

att)

Year

Dresden leading in both RGB and white

OLED Lighting Applications

source: Philips Lighting March 2004 GE demonstrator

Signage General lighting

Technology Roadmap (USDC)(Diffuse lighting)

OLLA project

OLLA EU 6th Framework Integrated Project initiated by Philips

OLLA: Organic LED for Lighting Applications

Aims:- Highly Efficient white OLED- Large Area OLED- Low-Cost manufacturing

Other German partners: - Siemens-Osram, Aixtron, Covion, HCStarck, Syntec, Novaled- FhG-IPMS, TU Dresden, Uni Kassel

about 15 further partners from other European Universities

Achieve Smooth Transition from R&D to production: Close Collaboration of Fraunhofer Society and Industry

Topics: OLED for Displays and LightingOrganic Solar CellsMemory and other Applications

Tools: - Gen 2 Inline Pilot Production Tool (Displays&Lighting)- Reel-to-Reel R&D tool

Location: New IPMS cleanroom: Virtually no building investment

A new Initiative: Center for Organic Materials and Electronic Devices Dresden (COMEDD)

Outline of COMEDD

Investment by FhG/state of saxony

Operations organized in projects

Projects are defined by advisory committee

OLED foundry does pilot manufacturing

Projects Tools

Inline Reel-to-Reel Manufacturing Manufacturing

Center for Organic Materials and Electronic Devices Dresden (COMEDD)

Advisory BoardFunding agencies,

FhG, Industry

COMEDD Operations

Funding agencies:SaxonyBMBF, EC

OLED Foundry

OLED have still a long way to go, but

Lifetime problem is close to being solved even for demanding applications

Efficiency: OLED displays: will beat all other FPDs OLED lighting: should be able to surpass fluorescent tube

COMEDD: New initiative to establish OLED manufacturing in Saxony

Conclusions

Acknowledgment

M. Pfeiffer, J. Blochwitz-Nimoth, G. He, G. Schwartz, K. Fehse, K. Walzer X. Zhou, J. Huang, A. Werner, A. Nollau, J. Drechsel, B. Mnnig, K. Harada, T. Fritz, B. Plnnigs, A. Beyer

J. Amelung, W. Jeroch, C. May, M. Schreil, M. Toerker, U. Todt (FhG-IPMS)

D. Alloway, P.A. Lee, N. Armstrong, Tucson (XPS/UPS) N. Karl (Stuttgart) D. Whrle (Bremen), J. Salbeck (Kassel), H. Hartmann (Merseburg) C.J. Bloom, M. K. Elliott (CSU)

BMBF, SMWA, SMWK, DFG, EC, FCI, NEDO