Novel Soft Materials: Organic Semiconductors

Transcription

1 JSPS Science Dialogue Novel Soft Materials: Organic Semiconductors X.T. HAO Prof. UENO s Lab Faculty of Engineering, Chiba University 21 st Century Center of Excellence Program

2 The route to research Transparent oxide semiconductors: Shandong University, China Organic light emitting devices: Institute of Materials Research and Engineering, Singapore Surface and interface of organic semiconductors: Prof. UENO s Lab, Faculty of Engineering, Chiba University, Japan

3 9.6million km 2, 1300 millions people Spring City--Jinan Bao Tu Spring

4 Transparent oxide semiconductors Shan Dong University Send out, Take in

5 Organic light emitting devices: Institute of Materials research & Engineering Transparent cathode Polymer layers Anode Substrate

6 Surface and interface of organic semiconductors: Prof. UENO s Lab

7 The route to research Find problems solve problems Improvement? More places more experiences Knowledgeable?

8 Novel Soft Materials: Organic Semiconductors

9 Outline Introduction Basic concepts in organic semiconductors Surface/interface of organic semiconductors Organic devices Summary

10 Resistivity difference =1,000,000,000,000,000,000,000,000 Discovery of organic semiconductors Japan, 1950 Pioneers: Akamatu and Inokuchi,

11 Current Research Status OLED Organic soft device Application Fundamental Synthesis of Organic Semiconductors A B C A Unified organic Device metal organic. Nanoscale structure and properties; electronic and electrical properties etc Pb Pb - Pb Pb Pb Nanoscale control of organic film growth Theory and experiment Molecular Scalpel/ Syn. Rad. h π Electron Electronic states and dynamics σ

12 One electron in one orbital Metal & Insulator [Quantum Effect] Two electrons in one orbital Animation contributed by Prof. H. FUKUYAMA

13 Motion of holes and electrons

14 Transport of charge carriers Motion of ball E E = 1 2 mv 2 = 2 P 2m P E Motion of electron E = E( P) P

15 Fermi Level The behavior of water in bucket and electrons in solid E F

16 E F φ VL Fermi Sea of electrons Metal Vacuum Bandgap E Conduction band E F φ VL Ionization energy Valence band Intrinsic semicond. Insulator Vacuum

17 Conductivity Ohm s Law V = IR σ =neµ R = ρl S σ 1 = ρ R = l σ S Carrier concentration Mobility

18 Conductivity Mobility Charge transfer rate k CT σ =neµ a µ = ea2 k B T k CT k CT = 2π h 1 t 2 4πλ reorg k B T exp λ reorg 4k B T µ We need smaller λ for higher µ t : Transfer integral (intermolecular interaction) λ reorg : Reorganization energy (hole-vibration coupling) λ reorg J. Cornil et al. Adv. Mater. 14, 726 (2002). Coropceanu et al.,theor. Chem. Acc. 110, 59 (2003). J.L.Bredas group, Chem.Rev.104, 4971 (2004).

19 Electronic interaction at surface/interface cathode e- transfer recombination h + transfer anode

20 Electron exchange Electron Organic molecule Metal atoms

21 Energy level alignment at interface Metal Organic Interface Molecular orientation reaction with metal distortion of electronic distribution existence of electric dipole

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23 Contact between metal and molecular solid Electron transfer Fermi level

24 Nobel Prize, 1921 Photoelectric effect

25 Photoelectric effect Photon Electron(E K )

26 E=hν-Φ Kinetic energy of photoelectron hν Binding energy (work function /metal) Solid Vacuum

27 e - velocity v hν + Potential is acting on photoelectron

28 v e - velocity v > v After the potential disappears, photoelectron travels without reducing its velocity.

29 Excited / vacuum level e - Work function (φ) E F e - E F Ionization potential IP E K = hv -IP e - hv Secondary electrons hv Secondary electrons E vac E F Fermi level E F Ionization potential UPS for metal UPS for organic film

30 High-resolution UPS -I Preparation chamber/organic He reefer He* X-ray Analyzer Preparation chamber/metal LEED/Auger Polarized VUV photon

31 High-resolution UPS -II Analyzer (R=300mm) (A-1, MBS-Toyama) Cleaning chamber (SPA-LEED) STM Spectrometer (M-1, MBS-Toyama) + He source (L-1, MBS) Preparation chamber

32 He* (MAES) source Chamber PIES/UPS Instrument and Characteristics of of PIES colddischarge type DP with L-N2Trap system TMP Q-MASS Measurment Chamber SP sample holder inlet for L-N2 Transfer Rod 180* hemi-spherical deflection type analyzer Sample Preparation Chamber Introduction Chamber DP with L-N2Trap system He I (UPS) source Chamber

33 PIES: Penning Ionization Electron Spectroscopy 2s 1s

34 Molecular orientation can be detected: PIES study P O Ti He*(2 3 S) MAES Intensity (arb. units) Gr(σ*) π Gr(π) n (O) state π π annealed as grown O Ti e - e - O Ti O Ti O Ti e - He* O Ti He* HOPG O Ti Ti O O Ti Ti O O Ti Binding Energy from E F sub (ev) 5 0

35 Organic devices: Organic light emitting devices Organic solar cells Organic thin film transistors etc Soft organic materials Flexible bendable devices

36 Organic light emitting diodes ~100nm (~0.0001mm) ~0.1-1mm 1mm =1,000,000nm

37 Organic solar cell

38 Basic structure of Organic LED Cathode Light Emitting Layer Hole Transport Layer Anode Substrate Cathode: metal material Emitter: organic materials Anode: metal, semiconductors Substrate: Rigid & flexible

39 cathode e- transfer recombination h + transfer anode Working Mechanism of OLED e- transfer h + transfer Luminescence E F HOMO LUMO - - E F

40 60 6 Sheet resistance resistivity Sheet resistance (Ω/sq) Resistivity (Ω cm) Hydrogen flow rate (sccm) 2

41 Conventional Flexible OLED approach Ag Ca EL ITO PET/barrier layer

42 Variable color OLEDs Non-cavity Top OLED Transparent cathode Organic stack ITO anode Transparent cathode Organic stack ITO anode Cavity Top OLED Substrate Mirror Mirror Substrate Non-cavity OLED Cathode mirror Organic stack ITO anode Substrate Cathode mirror Organic stack ITO anode Semitransparent mirror Substrate Cavity OLED

43 Variable color OLEDs Φ1+ Φ2+2ndλ=m2π λ1 λ2 λ3 λ1 λ2 λ3 ITO thickness: 21.7nm 43.3nm 65nm 86.7nm 108.3nm 130nm 151.1nm 173.3nm

44 High contrast OLED Cathode Organic stack TCO anode Optical destructive anode n(x) Transparent substrate Sunlight readable OLED display

45 Cathode Emitting layer HTL ITO glass

46 Technology and Advantages Rigid device Flexible device paper-like appearance high brightness low voltage etc ultra-thin, lightweight conformable shape low cost etc

47 Samsung s 21-inch and 40-inch OLED TV resolution :1920x1200 contrast ratio: 5000:1 resolution :1280 x 800 contrast ratio: 5000:1

48 Summary

49 Acknowledgement Japan Society for the Promotion of Science (JSPS) UENO s Lab: Prof. Ueno, Prof. Okudaira, Prof. Sakamoto, Dr. Kera, Other members

50 Thank you for your attention!