含雙氟苯并噻二唑與二噻吩并噻咯之D-A共軛分子之凝態行為與光電效能

Abstract

本研究合成含雙氟苯并噻二唑與二噻吩并噻咯之D-A低能隙共軛分子DTS(F2BTTH2)2，在有機異質接面太陽能電池上的應用上獲得4.2%的光電轉換效率，開路電壓0.86 V；有機場效電晶體之電荷遷移率為 2.6×10-2 cm2V-1S-1；並藉由熱差掃描卡計、二維廣角X光散射實驗、低掠角廣角X光散射實驗分析DTS(F2BTTH2)2在不同溫度、不同製程時的凝態結構。由熔融態降溫的過程中，DTS(F2BTTh2)2會先進入有序度低的介穩態LCN相(溫度<179℃)，隨著時間經過或溫度降至148℃以下時，DTS(F2BTTH2)2在基板上會進入有序度高的edge-on排列(phase II)。DTS(F2BTTH2)2結晶過程緩慢，在190℃進行剪切取向可協助分子排列成phase II。以旋轉塗佈法製成的薄膜除了有phase II排列也殘留了有序度較低LCN介穩相；反之，以PDMS誘導結晶法製成的DTS(F2BTTh2)2薄膜只具有明顯的phase II排列。PDMS誘導結晶法製成的薄膜具有較規則的有序排列，其電荷傳導率較旋轉塗佈所製成的薄膜高出一個級數。

In this study, dithienosilole and diflulorobenzothiadiazole were used as two asymmetry structure units in the preparation of the D-A low band gap bent-core molecule DTS(F2BTTh2)2. DTS(F2BTTh2)2 delivered OFET mobility of 2.6×10-2 cm2V-1S-1, and 4.2 % PCE with Jsc= 8.46 mA/cm2, Voc= 0.86 V, FF = 58.8% in solar cell using DTS(F2BTTH2)2:PCBM (1.5:1 w/w) active layer. DSC, 2D WAXS and GI WAXS and POM results indicated that DTS(F2BTTh2)2 has monotropic phase behavior. During the cooling process from molten state at 5 oC/min, DTS(F2BTTh2)2 assembled first into a metastable nematic liquid crystalline phase (LCN) at 179℃. The LCN phase further transformed into the thermodynamically stable phase, phase II, at 148℃. XRD results showed that phase II is a more ordered phase, and adopted edge-on orientation on substrate). Shearing DTS(F2BTTh2)2 on substrate assist molecules pack to phase II even at high temperature (190℃). In spin-casted thin film, both the more ordered phase II and less ordered LCN phases were found, suggesting that the assembling period is too short for the molecules to reach the most stable state (phase II) completely. PDMS-assisted crystal growth assisted DTS(F2BTTh2)2 to pack into phase. OFET devices prepared by PDMS assisted method delivered higher mobility than those prepared from spin-casting, because of the higher solid-state order in the active thin film.