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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 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.

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Presentation on theme: "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."— Presentation transcript:

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 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 App. Phys. Lett. 88, (2006) Jc ~ 0.01 mA/cm 2 Vertical space-charge-limited transistor Organic solid-state vacuum tube

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 O 2 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/cm 2 High aperture ratio by stacking

7 OLED driven by SCLT OLED efficiency 10 cd/A Jc = 50 mA/cm 2 Luminance = 5000 cd/m 2 Active matrix by blade coating HTL EML Emitter Base ETL Collector LiF PO-01-TB CBP PO-01-TB CBP P3HT PVP Al MoO 3 Al Glass NPB TBPi Al Ag OLED SCLT Al PEDOT MoO3 Cathode Light emission

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

9 Hot plate ITO Hot plate ITO Hot plate ITO Hot wind Hot plate ITO Organic layer Blade coating for OLED and vertical transistor J. Appl. Phys. 110, (2011) 4×4 cm 2 OLED

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

11 Progress of SCLT performance enough for OLED driving 國科會 卓越領航計劃 交大 特色計劃

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

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

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

15 2011 Breakthrough toward 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 cm 2 /Vs along the polymer backbone and the  -  orbital stacking and is lower than 2×10 -4 cm 2 /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 SAM treatment in OFETs Nature 5, 222, 2006 SAMs (Self-Assemble Monolayers): HMDS and OTS on SiO 2 for P3HT FET Gate Oxide P3HT SAM SD

20 Our idea : SAM on vertical sidewalls Conditions: 1.SAM: (a) HMDS and (b) OTS 1.Top injection : a)using symmetric EC metal to reduce built-in potential barrier b)Using MoO 3 /Al to adjust emitter work function as 5.3 eV CB by both spin coating and blade coating (without spinning)

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

22 Results: improved bulk mobility

23 Results: material analysis a b c d

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

25 2011 Breakthrough toward 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 1cm 2 Active Region 1 cm

28

29 Transistor Performance (Blade Coating PS Spheres) 小面積 (1mm 2 ) 元件輸出特性 On/off ratio ~ 大面積 (1cm 2 ) 元件輸出特性 On/off ratio ~ 5000

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

31 Other solution-processed OTFT Field-effect mobility Operation voltage On/off ratio Channel materialGate dielectric 2005 [JACS]0.004< 2 V100P3HTPolymer dielectric CPVP-C6 (thickness nm) 2005 [ APL]0.005< 2V200P3HTSAM 2006 [Nature Material] > 20 V> 10 6 PBTTTOTS-treated SiO [OE]0.017< 2 V3600P3HTPlasma oxidation on Al gate 2007 [APL]0.2 ~ 1.8> 10 V> 10 6 TIPSHMDS-treated SiO [JACS]0.1< 2 V10 5 P3HTIon-gel gate dielectric (for top gate); gel solution mixed with stirring over 12 hrs 2008 [Nature Materials, Adv. Mat.] < 3 V10 4 ~10 5 P3HT PQT-12 F8T2 Ion-gel gate dielectric (for top gate); slow process: solvent evaporated for 24 hrs and the ion-gel dried in vacuum over 2 days 2008 [Nature Material, JACS, APL] 1.5> 20 V> 10 6 diF-TESADTPFBT-treated gold electrodes with HMDS-treated SiO [Adv. Mat.]0.15> 30 V36700PETV12TPMMA, 500 nm 2009 [ Adv. Mat.] > 20 VN/APBTTT P3HT PQT-12 OTS-treated SiO [ Adv. Mat.]7-11> 20 V> 10 6 C8-BTBT or C10-DNTT CYTOP (Asahi Glass Co. for top-gate) 2011 [AIP Advances] 3.5> 20 V> 10 6 C8-BTBTFTS-treated SiO 2

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 within 1-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 Two Approaches: Fabricating OLED on top of SCLT Connecting large-area OLED with SCLT array panel HTL EML Emitter Base ETL Collector LiF PO-01-TB CBP PO-01-TB CBP P3HT PVP Al MoO 3 Al Glass NPB TBPi Al Ag OLED SCLT Al PEDOT MoO3 Cathode Light emission Glass OLED Light emission

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

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

39 Proposed Large Area Process ( 示意圖, 基板可放大 ) 100 um 10 um  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 within 1-V base voltage.


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