10. OLEDs and PLEDs - en.fh-muenster.de€¦ · 10.10 Polymer LED Spectra 10.11 Development of the Lifetime of PLEDs 10.12 Application Areas . Chapter OLEDs and PLEDs Slide 2 Incoherent

Chapter OLEDs and PLEDs Slide 1

Incoherent Light Sources Prof. Dr. T. Jüstel

10. OLEDs and PLEDs Content 10.1 Historical Development 10.2 Electroluminescent Molecules 10.3 Structure of OLEDs and PLEDs 10.4 Working Principle of OLEDs 10.5 Luminescence of Metal Complexes 10.6 Iridium Complexes 10.7 White OLEDs 10.8 PLEDs - Construction 10.9 Operation of a PLED 10.10 Polymer LED Spectra 10.11 Development of the Lifetime of PLEDs 10.12 Application Areas



10.1 Historical Development Some milestones • 1953 Observation of the electroluminescence of acridine orange

• 1960ties Studies of anthracene crystals

• 1987 Luminescent complexes: Al-8 hydroxychinolinate

• 1990 Luminescent polymers: poly(p-phenylenvinyliden) • 2009 Universal Display Corp. 102 lm/W Novaled/TU Dresden 90 lm/W Konica 64 lm/W Kodak 56 lm/W • 2012 Samsung: 55 inch OLED TV

Lit.: M. Dreußen, H. Bässler, Chemie in unserer Zeit 31 (1997) 76



10.2 Electroluminescent Molecules Anthracene

O

O

OO

OO

[Al(8-hydroxyquinolinate)3]

Polyphenyl vinylidene

Eu-complexes



10.3 Structure of OLEDs and PLEDs

Layer preparation by • Vapor deposition (sublimation) of the organic components and metals • Spin-coating from solutions

Substrate

Metal cathode

Organic layers

Cover Melting

Getter

Light

ITO

Metal contact

+ -



10.4 Working Principle of OLEDs Schematic construction Hole conductor

Emitter (organic phosphors)

Electron conductor



10.4 Working Principle of OLEDs Charge transport

(Al)

LiF

+ +

hole electron

and

singlet

tripletPhosphorescence

Fluorescence

Experimentally determined singlet fraction for Alq3 based OLEDs = 22 ± 3% Ref.: M.A. Baldo, et.al., Phys. Rev. B (1999)



Strong spin-orbit-coupling mixes singlet and triplet MLCT states, M = Ir, Pt, Os, Re, etc. MLCT = metal to ligand charge transfer, LC = ligand centered

Luminescence

1MLCT

3MLCT

S0 ground state

Ligand centered triplet

3LC

State mixing

+

hole electron

or

singlet

triplet

10.4 Physical Principle of an OLED Energy Flow



10.5 Luminescence of Metal Complexes

Absorption (ligand) • 1π−π → 1π−π* • 1π−π* → 3π−π* Ligand-metal energy transfer • 3π−π → 5D1, 5D0 (Eu3+) Emission (metal) • 5D0 (Eu3+) → 7FJ (Eu3+) • 5D1 and 5D2 levels are quenched

due to electron-phonon coupling (multi-phonon-relaxation)

3ππ∗

5D0

5D1

5D2

7JF

CT1 ∗ππ

hν nr nr

ISC

Energy level diagram of Eu3+-complexes



10.6 Iridium Complexes

Advantages of Ir3+ complexes • Strong spin-orbit coupling

Emission spectrum of Ir3+ complexes • MLCT and 3π-π* transitions • Position of the HOMO and thus the emission

bands can be determined by the ligands and controlled by substitutents on the ligands

[(4,6-F2ppy)2Ir(pic)] pic = picolinat [Ir(ppy)3] ppy = phenylpyridine

[(pch)2Ir(acac)] pch = phenylquinolinate

acac = acetylacetonate



450 500 550 600 6500,0

0,2

0,4

0,6

0,8

1,0

PL In

tens

ity (a

rb. u

nits

)

Wavelength [nm]

(ppy)2Ir(acac) (F2-ppy)2Ir(acac) (F2-ppy)2Ir(pic)

N

IrH,F

H,F

O

O

2

N

IrF

F

O

N

O

2

0.0 0.2 0.4 0.6 0.80.0

0.2

0.4

0.6

0.8

1

2

3 (F2ppy)2Ir(pic)

(F2ppy)2Ir(acac)

ppy2Ir(acac)

x

[(4,6-F2-ppy)2Ir(L)] - Photoluminescence and color points

10.6 Iridium Complexes



Substrate

Matrix:Green Matrix:Red

HTL p-HIL ITO

ETL Matrix:Blue

Al n-EIL

Emitter Colour Efficiency Lifetime

Fluorescent

R + ++

G + ++

B + +

Phosphorescent

R ++ +

G ++ +

B + o

Expected external quantum efficicency without light outcoupling measures Full fluorescent RGB 5-10% Full phosphorescent RGB 20% Hybrid: B fluorescent 16% R+G phosphorescent

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,80,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

10.7 White OLEDs - Options

Source: Philips Lighting Aachen



10.7 White OLEDs - Light Out-coupling

External radiation: about 20 - 30% only

Guided modes Emitter molecule

Glass substrate

Cathode (mirror)

Organic layers Wave

guided light




10.8 Polymer LEDs - Construction

n

O

O Poly(dialkoxy-p-phenylenevinylene) “PPV”




-

+

- +

-

+

- +

1: Injection 2: Intrachain transport

3: Interchain transport 4: Recombination

Glass ITO

PPV

Ca

Glass

Glass Glass ITO

PPV

Ca

10.9 Operation of a Polymer LED



Wavelength [nm]450 500 550 600 650 700 750 800

EL in

tens

ity [a

.u.]

0

2000

4000

6000

8000Eye Sensitivity Curve

10.10 Polymer LED Spectra Emission spectra of some polymers




10.11 Development of the Lifetime of PLEDs

1

10

100

1000

10000

100000

1993 1995 1997 1999 2001

Life

time

[h]

Room temperature70 Celcius

Data for 20 cd/m2 brightness

Degradation due to O2 and H2O ⇒ Encapsulation is necessary



10.12 Application Areas Flexible displays without backlight • Shaver displays • Digital cameras • Warning signs • OLED TVs/monitors • Light tiles • Smart phones

Philips Lumiblade

Documents

10. OLEDs and PLEDs - en.fh-muenster.de€¦ · 10.10 Polymer LED Spectra 10.11 Development of the Lifetime of PLEDs 10.12 Application Areas . Chapter OLEDs and PLEDs Slide 2 Incoherent