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
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
9.6million km 2, 1300 millions people Spring City--Jinan Bao Tu Spring
Transparent oxide semiconductors Shan Dong University Send out, Take in
Organic light emitting devices: Institute of Materials research & Engineering Transparent cathode Polymer layers Anode Substrate
Surface and interface of organic semiconductors: Prof. UENO s Lab
The route to research Find problems solve problems Improvement? More places more experiences Knowledgeable?
Novel Soft Materials: Organic Semiconductors
Outline Introduction Basic concepts in organic semiconductors Surface/interface of organic semiconductors Organic devices Summary
Resistivity difference 10 24 =1,000,000,000,000,000,000,000,000 Discovery of organic semiconductors Japan, 1950 Pioneers: Akamatu and Inokuchi,
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
One electron in one orbital Metal & Insulator [Quantum Effect] Two electrons in one orbital Animation contributed by Prof. H. FUKUYAMA
Motion of holes and electrons
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
Fermi Level The behavior of water in bucket and electrons in solid E F
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
Conductivity Ohm s Law V = IR σ =neµ R = ρl S σ 1 = ρ R = l σ S Carrier concentration Mobility
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).
Electronic interaction at surface/interface cathode e- transfer recombination h + transfer anode
Electron exchange Electron Organic molecule Metal atoms
Energy level alignment at interface Metal Organic Interface Molecular orientation reaction with metal distortion of electronic distribution existence of electric dipole
Contact between metal and molecular solid Electron transfer Fermi level
Nobel Prize, 1921 Photoelectric effect
Photoelectric effect Photon Electron(E K )
E=hν-Φ Kinetic energy of photoelectron hν Binding energy (work function /metal) Solid Vacuum
e - velocity v hν + Potential is acting on photoelectron
v e - velocity v > v After the potential disappears, photoelectron travels without reducing its velocity.
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
High-resolution UPS -I Preparation chamber/organic He reefer He* X-ray Analyzer Preparation chamber/metal LEED/Auger Polarized VUV photon
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
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
PIES: Penning Ionization Electron Spectroscopy 2s 1s
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 15 10 Binding Energy from E F sub (ev) 5 0
Organic devices: Organic light emitting devices Organic solar cells Organic thin film transistors etc Soft organic materials Flexible bendable devices
Organic light emitting diodes ~100nm (~0.0001mm) ~0.1-1mm 1mm =1,000,000nm
Organic solar cell
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
cathode e- transfer recombination h + transfer anode Working Mechanism of OLED e- transfer h + transfer Luminescence E F HOMO + + + + + + + + + - + - - - - - - LUMO - - E F - - - - - - - - + + + + + + +
60 6 Sheet resistance resistivity Sheet resistance (Ω/sq) 50 40 30 5 4 3 Resistivity (Ω cm) 20 0.0 0.5 1.0 1.5 2.0 Hydrogen flow rate (sccm) 2
Conventional Flexible OLED approach Ag Ca EL ITO PET/barrier layer
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
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
High contrast OLED Cathode Organic stack TCO anode Optical destructive anode n(x) Transparent substrate Sunlight readable OLED display
Cathode Emitting layer HTL ITO glass
Technology and Advantages Rigid device Flexible device paper-like appearance high brightness low voltage etc ultra-thin, lightweight conformable shape low cost etc
Samsung s 21-inch and 40-inch OLED TV resolution :1920x1200 contrast ratio: 5000:1 resolution :1280 x 800 contrast ratio: 5000:1
Summary
Acknowledgement Japan Society for the Promotion of Science (JSPS) UENO s Lab: Prof. Ueno, Prof. Okudaira, Prof. Sakamoto, Dr. Kera, Other members
Thank you for your attention!