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有機光電半導體材料及其未來之應用

有機光電半導體材料及其未來之應用. 郭 宗 枋 助理教授. Institute of Electro-Optical Science and Engineering, National Cheng Kung University, Tainan, Taiwan 701 成功大學 光電科學與工程研究所 01/16/2007. Outlines. Semiconductors Organic semiconductors (energy and delocalization of charge carriers) OLEDs and PLEDs 基礎原理和應用

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有機光電半導體材料及其未來之應用

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  1. 有機光電半導體材料及其未來之應用 郭 宗 枋 助理教授 Institute of Electro-Optical Science and Engineering, National Cheng Kung University, Tainan, Taiwan 701 成功大學 光電科學與工程研究所 01/16/2007

  2. Outlines • Semiconductors • Organic semiconductors (energy and delocalization of charge carriers) • OLEDs and PLEDs 基礎原理和應用 • Organnic photovoltaic and solar cells • Conclusions NCKU Institite of Electro-Optical Science & Engineering

  3. Fundamental science of inorganic semiconductors NCKU Institite of Electro-Optical Science & Engineering

  4. Typical Semiconducting Materials NCKU Institite of Electro-Optical Science & Engineering

  5. (a) a conductor (b) a semiconductor (c) an insulator Energy Band Diagram of a conductor, semiconductor, and insulator NCKU Institite of Electro-Optical Science & Engineering

  6. Beginning of orgnaic semiconductor (πbonding) Side-by-Side Bonding NCKU Institite of Electro-Optical Science & Engineering

  7. CH CH CH 單鍵 雙鍵 CH CH CH Conjugated (共軛): alternatively double-single bonds NCKU Institite of Electro-Optical Science & Engineering

  8. Band Gap ……….. …… Bang Gap of Polyacetylene NCKU Institite of Electro-Optical Science & Engineering

  9. Alternating single-double bonds Delocalized  electron cloud Sigma bond http://www.cdtltd.co.uk • Conjugated polymer NCKU Institite of Electro-Optical Science & Engineering

  10. PPP PA n n Eg = 3.0 eV Eg = 1.4 eV Through the structure engineering, polymers with different emitting colors were synthesized. PPV R 1 R 1 n n Eg = 2.4 eV R R 2 2 Eg = 2.4 eV O O n Eg = 2.1 eV Creating new materials from old materials NCKU Institite of Electro-Optical Science & Engineering

  11. Delocalization of Charge Carriers in Polyacetylene Localized! Charge cannot go anywhere!!! Delocalized! Charge carriers can move around!!! NCKU Institite of Electro-Optical Science & Engineering

  12. Delocalization and Transport of Charge Carriers NCKU Institite of Electro-Optical Science & Engineering

  13. Conjugated Polymers: Basic Materials and Chemistry • Conduction polymers: • Polyacetylene, Polyaniline, PEDOT/PSS… etc. • Semiconducting polymers: • Polythiophenes, Oligothiophenes… etc. • Light-emitting/Photovoltaic Polymers: • Poly-(para-phenylene-vinylene), Poly(para-phenylene), Polyfluorene… etc. NCKU Institite of Electro-Optical Science & Engineering

  14. Scientific Interest in Organic Materials • 1950’s – steady work on crystalline organics starts • 1970’s – organic photoconductors (Xerography) • 1980’s – organic non-linear optical materials • 1987 – Kodak first published the efficient organic light-emitting devices (OLED) • 1990 – Cambridge groups publish the first polymer light-emitting diodes (PLED) • Since then, the field has dramatically expanded both commercially and scientifically, including OLED, PLED, transistors, potovoltaic, solar cells……… NCKU Institite of Electro-Optical Science & Engineering

  15. What are the OLEDs? • Invented by Dr. Ching W Tang （鄧青雲博士）(kodak) 1987年 • OLED 全名叫做有機發光二極體 (Organic Light-Emitting Diode) • 部分國外又稱 OEL為有機電激光顯示 (Organic Electroluminescence Display) NCKU Institite of Electro-Optical Science & Engineering

  16. OLED Basic Device Configuration • Double layers structure • 電洞傳輸層-Hole Transport (injection) Layer (HTL) • 電子傳輸層– Electron Transport Layer (ETL) • 發光層- Emitting Layer (EML) NCKU Institite of Electro-Optical Science & Engineering

  17. First OLED Invented by Dr. Ching W Tang (kodak) 1987 NCKU Institite of Electro-Optical Science & Engineering

  18. Absorption, Fluorescence & Phosphorescence Process NCKU Institite of Electro-Optical Science & Engineering

  19. Photophysics process carrier separation e-/h+ carrier injection dissociation recombination dissociation Intersystem crossing Singlet excitons Triplet excitons T-T annihilation fluorescence phosphorescence hν1 hν2 non-radiation heat ground state NCKU Institite of Electro-Optical Science & Engineering

  20. _ Cathode ETL HTL + Anode ITO Glass or PET substrate _ _ _ _ _ _ _ _ + + + + + + + + Operation of OLEDs NCKU Institite of Electro-Optical Science & Engineering

  21. Single layer device PLED Double layer device OLED Double layer device Electroluminescence of O/PLED NCKU Institite of Electro-Optical Science & Engineering

  22. 1/ 2 1/ 2 Mechanism of Electroluminescence NCKU Institite of Electro-Optical Science & Engineering

  23. Intersystem crossing (ISC) S1 T1 Fluorescence Phosphorescence S0 Ground state Fluorescence and Phosphorescence Singlet exciton Triplet exciton 25% 75% Decay from singlet allowed by symmetry: fast and often efficient. Decay from triplet disallowed by symmetry: slow and usually inefficient. NCKU Institite of Electro-Optical Science & Engineering

  24. Device preparation ITO/Glass substrate Vacuum<10-5 torr Organic materials Lecture note of Prof. Chou, NTU Phys. NCKU Institite of Electro-Optical Science & Engineering

  25. What are PLEDs? • Invented by Richard. H. Friend (University of Cambridge, Cavendish Laboratory) 1990年 • PLED 全名叫做高分子發光二極體(Polymer Light-Emitting Diode) • Usually for single layer device configuration NCKU Institite of Electro-Optical Science & Engineering

  26. They used Al as the cathode material at that time. First PLED Invented by Richard. H. Friend (Cambridge University, Cavendish Laboratory)1990 NCKU Institite of Electro-Optical Science & Engineering

  27. Synthetic Route to PPV J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks, K. Mackay, R. H. Friend, P. L. Burns, and A. B. Holmes, Nature, 347, 539 (1990). NCKU Institite of Electro-Optical Science & Engineering

  28. Schematic Energy Level Diagram NCKU Institite of Electro-Optical Science & Engineering

  29. MEH-PPV O Pre-cleaned ITO/glass substrate Cathode deposition * Eg=2.1eV Orange-red or yellow n * O PEDOT:PSS Processing for the fabrication of a typical PLED Spin coating PEDOT layer & baking Spin coating MEH-PPV layer & baking NCKU Institite of Electro-Optical Science & Engineering

  30. Biased device Before bias PLED Devices at NCKU NCKU Institite of Electro-Optical Science & Engineering

  31. Why they are so important? Self-luminescent No viewing angle limitation Thin, Light weight Low operation voltage Flexible substrate application http://www.nobel.se/chemistry/laureates/2000/illpres/7.html NCKU Institite of Electro-Optical Science & Engineering

  32. 20 inches, amorphous Si, active matrix, full color OLED display WXGA (1280 x 768 pixels), 25 W, 300 cd/m2, CMO 03/12/2003 Ink-jet printed EL display, Toshiba and Epson2002 Recent progress of EL Panels Kodak digital camera, available on April 2003 NCKU Institite of Electro-Optical Science & Engineering

  33. Inorganic photovoltaic cell Reasons for organic solar cells Organic solar cells: moderate efficiencies and very low cost NCKU Institite of Electro-Optical Science & Engineering S.E. Shaheen, D.S. Ginley, G.E. Jabbour, Mrs. Bull., 30, pp.10-18(2005).

  34. hν Flexible Donor-acceptor type solar cells A Flexible, printed plastic solar cell with high efficiency made by SIMENS AG NCKU Institite of Electro-Optical Science & Engineering

  35. Metal electrode Donor + Acceptor ITO hν Workingprincipleoforganicsolar cell A Donor - Acceptor type bulk heterojunction solar cell LUMO Donor e- LUMO Acceptor hν e- Donor-P3HT e- EF h+ Metal electrode (Al, Ca/Al etc.) ITO/PEDOT h+ h+ h+ HOMO Donor HOMO PCBM Acceptor-PCBM NCKU Institite of Electro-Optical Science & Engineering

  36. J (photo-current density) – V (Bias) curves for devices with Al and Ca/Al as the cathodes • Incident power of 90mW/cm2

  37. Conclusions • Organic electronics乃是一項跨領域的學科，涵蓋半導體元件物理、基礎物理、電機、化學、材料…而基礎物理化學的基礎更是為重要。 • Flexible devices (軟性電子) 將是未來科技的一項研究重點，此乃organic electronics之發展強項。 NCKU Institite of Electro-Optical Science & Engineering

  38. Future of Information Display NCKU Institite of Electro-Optical Science & Engineering

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