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特色研究計畫 - 以刮刀塗佈技術製備垂直式有機電晶體用於低成本有機發光顯示器

特色研究計畫 - 以刮刀塗佈技術製備垂直式有機電晶體用於低成本有機發光顯示器. 交通大學物理研究所 孟心飛 交通大學光電系 冉曉雯 有機半導體實驗室研究生 : 趙寅初、王凱瑞、徐永軒、羅芳財、黃建豪、呂季遠、林洪正、蔡武衛. Limits of organic field-effect transistor. Long channel length ~ 5 micron High operation voltage ~ 10 V Low output current. Organic semiconductor.

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特色研究計畫 - 以刮刀塗佈技術製備垂直式有機電晶體用於低成本有機發光顯示器

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  1. 特色研究計畫-以刮刀塗佈技術製備垂直式有機電晶體用於低成本有機發光顯示器特色研究計畫-以刮刀塗佈技術製備垂直式有機電晶體用於低成本有機發光顯示器 交通大學物理研究所 孟心飛 交通大學光電系冉曉雯 有機半導體實驗室研究生: 趙寅初、王凱瑞、徐永軒、羅芳財、黃建豪、呂季遠、林洪正、蔡武衛

  2. Limits of organic field-effect transistor Long channel length ~ 5 micron High operation voltage ~ 10 V Low output current Organic semiconductor

  3. Vertical space-charge-limited transistor Organic solid-state vacuum tube Jc ~ 0.01 mA/cm2 App. Phys. Lett. 88, 223510(2006)

  4. Space-charge-limited current (SCLC) • No background carrier • Current by injected carriers • Organic semiconductor valence band in place of vacuum

  5. Grid base fabrication polystyrene nano-spheres as mask O2 plasma

  6. Advantages of SCLT • Short vertical channel ~ 300 nm • Low operation voltage ~ 2 V • No lithography for base grid • OLED driving • High current density ~ 100 mA/cm2 • High aperture ratio by stacking

  7. OLED driven by SCLT Ag Al Light emission TBPi Cathode PO-01-TB CBP P3HT LiF ETL NPB Al PVP Al Al EML OLED HTL MoO3 PEDOT MoO3 Al Al Collector SCLT Glass Base Emitter OLED efficiency 10 cd/A Jc = 50 mA/cm2 Luminance = 5000 cd/m2 Active matrix by blade coating

  8. Multi-layer blade coating of organic semiconductors energy Electron blocking cathode Emissive Hole blocking anode 50 -100 micron gap moving Rapid evaporation Polymer solution Gap Polymer film (wet) Polymer film (dry) Appl. Phys. Lett. 93, 153308 (2008) ITO Substrate Hot plate Emission layer • Multi-layer solution deposition for high efficiency • Arbitrary solvent • Large area uniformity • Low material waste • Compatible with roll-to-roll process

  9. Blade coating for OLED and vertical transistor ITO ITO Hot plate Hot plate Organic layer Hot wind 4×4 cm2 OLED ITO ITO Hot plate Hot plate J. Appl. Phys. 110, 094501 (2011)

  10. Other applications RFID Pressure sensor array Short channel length Short carrier transit time High frequency App. Phys. Lett. 95, 253306 (2009)

  11. Progress of SCLT performanceenough for OLED driving 2008-2012 國科會 卓越領航計劃 2011 - 交大 特色計劃

  12. Enhancing the base control Appl. Phys. Lett., 97, 223307, 2010

  13. Enhancing the base control Appl. Phys. Lett. 98, 223303, 2011

  14. 2011 Breakthroughtoward a real technology • Jump in collector current • Organic semiconductor blade coating • Self-assembled monolayer • PS sphere by blade coating

  15. 2011 Breakthroughtoward a real technology • Jump in collector current • Organic semiconductor blade coating • Self-assembled monolayer • PS sphere by blade coating

  16. Conduction in Organic Semiconductors Van der Walls forces hold molecules together Charge transport is dependent on -bonding orbitals and quantum mechanical wave-function overlap (by hopping). Effective mobility increases with increasing temperature and increasing carrier concentration Space-charge-limited current:

  17. Anisotropic Transport • Charge transport in most organic semiconductor including conjugated polymers is anisotropic. Field-effect hole mobility in P3HT is higher than 0.1 cm2/Vs along the polymer backbone and the - orbital stacking and is lower than 2×10-4 cm2/Vs along the insulating side chain • E.g. P3HT: poly(3-hexylthiophene)

  18. Q: How to improve the output current in organic transistor ? A: Improving molecular packing in the right direction! • For conventional FET: • Current flows in lateral direction. • Edge-on direction is required to obtain high mobility. • Reported methods: • Using high boiling point solvent to improve molecular packing • Using solvent annealing to improve molecular packing • Using SAM to control orientation !!

  19. S D P3HT SAM Oxide Gate SAM treatmentin OFETs • Nature 5, 222, 2006 • SAMs (Self-Assemble Monolayers): HMDS and OTS on SiO2 for P3HT FET

  20. Our idea : SAM on vertical sidewalls • Conditions: • SAM: (a) HMDS and (b) OTS • Top injection : • using symmetric EC metal to reduce built-in potential barrier • Using MoO3/Al to adjust emitter work function as 5.3 eV • P3HT @ CB by both spin coating and blade coating (without spinning)

  21. Results: improved pore filling • After OTS treatment, pore surface becomes hydrophilic OTS treated, spin coating STD (no SAM), spin coating STD, blade coating

  22. Results: improved bulk mobility

  23. Results: material analysis a b c d

  24. Results: transistor performances a VCE=-2 V b c

  25. 2011 Breakthroughtoward a real technology • Jump in collector current • Organic semiconductor blade coating • Self-assembled monolayer • PS sphere by blade coating  compatible to roll-to-toll process

  26. Blade coating PS spheres (a) PS sphere blade coating (b) Conventional Dipping Method

  27. PS Sphere Distribution in 1cm2 Active Region 1 2 1 cm 3 1 cm

  28. 3 1 2

  29. Transistor Performance(Blade Coating PS Spheres) 小面積(1mm2)元件輸出特性 On/off ratio ~ 40000 大面積(1cm2)元件輸出特性 On/off ratio ~ 5000

  30. Connected OLED/SCLT Al/MoO3 pattern Top Emitter Off state On state Total voltage : 6 V (across OLED and SCLT) ON state: Base voltage = -0.9 V; OFF state: Base voltage = 0 V 42-b

  31. Other solution-processed OTFT

  32. Summary • With high output current , low operation voltage and high on/off current ratio, vertical transistor SCLT is one of the best solution processed transistor in the world. • Blade coating is successfully demonstrated on OLED and SCLT. Particularly, blade coating PS spheres facilitates the roll-to-roll large area nanostructure colloidal lithography . • Solution processed OLED can be switched on and off by SCLT within1-V base voltage.

  33. Future Work • Develop process for integrated solution-processed OLED/SCLT. • Develop large-area array process for SCLT. • Integrate large-area SCLT array with large-area OLED to realize low-cost e-book (based on blade coating process). • Proposed process is introduced hereafter.

  34. Integrated OLED / SCLT Ag Al Light emission TBPi Cathode PO-01-TB CBP P3HT LiF ETL NPB Al Al PVP Al EML OLED HTL MoO3 PEDOT MoO3 Al Al Collector SCLT Glass Light emission Base Glass OLED Emitter Glass Two Approaches: Fabricating OLED on top of SCLT Connecting large-area OLED with SCLT array panel

  35. 100 um 10 um Proposed Large Area Process(示意圖,基板可放大) Tentative process to define the bottom metal electrode: Low-end lithography with lift-off process, blanket bar coating (similar to blade coating) or interference lithography

  36. 100 um 10 um Proposed Large Area Process(示意圖,基板可放大)  PVP coating and cross-linking  10-um wide PR line formation (low-end photolithography, blanket bar coating or interference lithography)  PS spheres coating on PVP

  37. 100 um 10 um Proposed Large Area Process(示意圖,基板可放大) •  Base metal deposition with PR lift-off process • Removing PS spheres by roller taping

  38. 100 um 10 um Proposed Large Area Process(示意圖,基板可放大) •  Plasma etch through nanometer holes • SAM treatment on nanometer holes • P3HT coating

  39. 100 um 10 um Proposed Large Area Process(示意圖,基板可放大) •  Passivation layer formation • Pixel contact via formation and metal coating (patterned by liftoff process) • Then: fabricating large-area OLED on top of array panel or connecting array panel with OLED (on the other substrate)

  40. Demonstration • PS sphere blade coating process. • Solution processed OLED switched on and off by SCLT within1-V base voltage.

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