合成以寡噻吩(Oligothiophene)為電子予體之受-予-受小分子應用於異質接面太陽能電池元件之研究

Abstract

本研究我們使用Oligothiophene(寡噻吩)作為主鏈合成小分子A-D-A結構，電子受體為具有良好吸光性的thiobarbituric acid (TB)雜環，在電子予體上我們加入不同長度之碳鏈側鏈合成小分子BT-TB3T、DOBT-TB3T以及DDBT-TB3T。我們發現不同之碳鏈側鏈長對於小分子材料之熱性質、吸光特性、分子間堆疊能力以及元件特性皆有所影響。BT-TB3T分子間作用力較強，退火後具有較強之結晶特性，分子間排列出現face-on與edge-on方向之堆疊，因此光電流(Jsc)良好(8.44 mAcm-2)，混摻PC61BM製成元件光電轉換效率(PCE)達3.8 %；DOBT-TB3T因加入octyl(C8)之側鏈，分子間作用力受碳鏈之影響變弱，退火後結晶能力較差但開路電壓(Voc)提升(0.95 V)，混摻PC61BM製成元件光電轉換率為(PCE)3.6 %；DDBT-TB3T加入最長dodecyl(C12)之側鏈嚴重影響分子間堆疊造成退火後仍結晶能力差，混摻PC61BM製成元件光電轉換效率(PCE)僅達1.14 %。

In this study, we synthesized three A-D-A typed small molecules, BT-TB3T、DOBT-TB3T and DDBT-TB3T, composed of 2,2’-bithiophene(BT), 4,4'-dioctyl-2,2'-bithiophene(DOBT),and 4,4'-didodecyl-2,2'-bithiophene(DDBT) as central donor core, respectively, terthiophene as bridge, and thiobarbituric acid as electron acceptor. Those molecules display broad absorption width in visible region .By varying alkyl chain, we found that side chain length on the core affect their intermolecular stacking capabilities, thermal properties, and light absorption properties; hence, it also determent the device characteristics. BT-TB3T show strongly intermolecular forces, after annealing with a strong ability to crystallize; besides, the orientation of stacking are face-on and edge-on direction, which is favor morphology for OPVs. The devices incorporated BT-TB3T and PC61BM show highly Jsc (8.44 mAcm-2), and result the highest efficiency (3.8 %).On the contrary, DOBT-TB3T, featuring octyl chains on core, show higher Voc (0.95 V) and less Jsc (7.09 mAcm-2)because of weak intermolecular forces arising from the influence of side chains. On the other hand, DDBT-TB3T which has longest alky chain exhibit poor crystallinity; thus, PCE is just only 1.14% when it was blend with PC61BM.