10. OLEDs and PLEDs. Content

Transcription

1 Content 10. LEDs and PLEDs 10.1 Historical Development 10.2 Electroluminescent Molecules 10.3 Structure of LEDs and PLEDs 10.4 Working Principle of LEDs 10.5 Luminescence of Metal Complexes 10.6 Iridium Complexes 10.7 White LEDs 10.8 PLEDs - Construction 10.9 peration of a PLED Polymer LED Spectra Development of the Lifetime of PLEDs Application Areas Slide 1

2 Some milestones 10.1 Historical Development 1953 bservation 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 LED TV Lit.: M. Dreußen, H. Bässler, Chemie in unserer Zeit 31 (1997) 76 Slide 2

3 10.2 Electroluminescent Molecules Anthracene Polyphenyl vinylidene [Al(8-hydroxyquinolinate) 3 ] Eu-complexes Slide 3

4 10.3 Structure of LEDs and PLEDs Light Substrate - Melting Cover Getter + IT Metal contact Metal cathode rganic layers Layer preparation by Vapor deposition (sublimation) of the organic components and metals Spin-coating from solutions Slide 4

5 Schematic construction 10.4 Working Principle of LEDs Hole conductor Electron conductor Emitter (organic phosphors) Slide 5

6 Charge transport 10.4 Working Principle of LEDs hole electron (Al) + + and triplet singlet Experimentally determined singlet fraction for Alq 3 based LEDs = 22 ± 3% Ref.: M.A. Baldo, et.al., Phys. Rev. B (1999) LiF Phosphorescence Fluorescence Slide 6

7 10.4 Physical Principle of an LED Energy Flow hole electron + triplet or singlet 1 MLCT 3 MLCT Ligand centered triplet 3 LC State mixing Luminescence S 0 ground state Strong spin-orbit-coupling mixes singlet and triplet MLCT states, M = Ir, Pt, s, Re, etc. MLCT = metal to ligand charge transfer, LC = ligand centered Slide 7

8 10.5 Luminescence of Metal Complexes Energy level diagram of Eu 3+ -complexes 1 ππ 3 ππ ISC CT 5 D 2 5 D 1 Absorption (ligand) 1 π π 1 π π* 1 π π* 3 π π* 5 D 0 Ligand-metal energy transfer 3 π π 5 D 1, 5 D 0 (Eu 3+ ) hν nr nr 7F J Emission (metal) 5 D 0 (Eu 3+ ) 7 F J (Eu 3+ ) 5 D 1 and 5 D 2 levels are quenched due to electron-phonon coupling (multi-phonon-relaxation) Slide 8

9 [Ir(ppy) 3 ] 10.6 Iridium Complexes ppy = phenylpyridine [(4,6-F 2 ppy) 2 Ir(pic)] pic = picolinat Advantages of Ir 3+ complexes Strong spin-orbit coupling [(pch) 2 Ir(acac)] pch = phenylquinolinate acac = acetylacetonate Emission spectrum of Ir 3+ complexes MLCT and 3 π-π* transitions Position of the HM and thus the emission bands can be determined by the ligands and controlled by substitutents on the ligands Slide 9

10 10.6 Iridium Complexes [(4,6-F 2 -ppy) 2 Ir(L)] - Photoluminescence and color points PL Intensity (arb. units) 1,0 0,8 0,6 0,4 0,2 (ppy) 2 Ir(acac) (F 2 -ppy) 2 Ir(acac) (F 2 -ppy) 2 Ir(pic) H,F N Ir H,F N Ir F F 2 ppy 2 Ir(acac) (F 2 ppy) 2 Ir(acac) N 0, Wavelength [nm] (F 2 ppy) 2 Ir(pic) x Slide 10

11 10.7 White LEDs - ptions Emitter Colour Efficiency Lifetime R + ++ Fluorescent G + ++ B + + R ++ + Phosphorescent G ++ + B + o 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0,0 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 Expected external quantum efficicency without light outcoupling measures Full fluorescent RGB 5-10% Full phosphorescent RGB 20% Hybrid: B fluorescent 16% R+G phosphorescent Source: Philips Lighting Aachen Al n-eil ETL Matrix:Blue Matrix:Green Matrix:Red HTL p-hil IT Substrate Slide 11

12 10.7 White LEDs - Light ut-coupling External radiation: about 20-30% only Glass substrate rganic layers Emitter molecule Guided modes Wave guided light Cathode (mirror) Source: Philips Lighting Aachen Slide 12

13 10.8 Polymer LEDs - Construction n Poly(dialkoxy-pphenylenevinylene) PPV Source: Philips Lighting Aachen Slide 13

14 peration of a Polymer LED 1: Injection 2: Intrachain transport Ca PPV + IT Glass - + Glass 3: Interchain transport 4: Recombination Ca - + Glass PPV IT - + Glass Slide 14

15 Emission spectra of some polymers Polymer LED Spectra 8000 Eye Sensitivity Curve 6000 EL intensity [a.u.] Wavelength [nm] Source: Philips Lighting Aachen Slide 15

16 10.11 Development of the Lifetime of PLEDs Lifetime [h] Room temperature 70 Celcius Data for 20 cd/m 2 brightness Degradation due to 2 and H 2 Encapsulation is necessary Slide 16

17 Flexible displays without backlight Shaver displays Digital cameras Warning signs LED TVs/monitors Light tiles Smart phones Application Areas Philips Lumiblade Slide 17