Two isomeric A-D-A type small molecules (SMs) of BDTx-2TVTDPP and BDTy-2TVTDPP were designed and synthesized, which contain different donor (D) center of substituted benzodithiophene (BDT) in backbone, and the same acceptor (A) and bridged units of diketopyrrolopyrrole (DPP) and thienylenevinylenethiophene (TVT), respectively. Their thermal stability, crystallinity, film morphology and photoelectronic properties were primarily investigated. It was found the BDTx-2TVTDPP with 2,6-substituted BDT unit exhibited a pronouncedly red-shifted and enhanced absorption in solid state and a better crystallinity. In contrast, the BDTy-2TVTDPP with 4,8-substituted BDT unit in backbone exhibited better solubility, deeper HOMO energy level and more smoothed blend film morphology. As a result, the solution-processing BDTy-2TVTDPP based solar cells displayed better photovoltaic properties than the BDTx-2TVTDPP based ones using fullerene derivatives (PC₆₁BM or PC₇₁BM) as electron acceptor. A power conversion efficiency maximum of 2.85% was obtained in the BDTy-2TVTDPP based cells, which is 1.8 times that of the BDTx-2TVTDPP based cells. This study indicates that changing the substituted positions of BDT is available to significantly improve photovoltaic properties for its resulting SMs.

中文翻译：

---

具有异构苯并二噻吩核的ADA型小分子：异构体的合成及其对光电性能的影响

设计并合成了BDTx-2TVTDPP和BDTy-2TVTDPP的两种ADA型异构小分子（SM），它们在主链上含有不同的取代苯并二噻吩（BDT）供体（D）中心，相同的受体（A）和桥联单元。二酮吡咯并吡咯（DPP）和噻吩亚乙烯基噻吩（TVT）。主要研究了它们的热稳定性，结晶度，膜形态和光电性能。发现具有2，6-取代的BDT单元的BDTx-2TVTDPP在固态下表现出明显的红移和增强的吸收以及更好的结晶度。相比之下，在主链中具有4,8-取代的BDT单元的BDTy-2TVTDPP表现出更好的溶解度，更深的HOMO能级和更平滑的共混膜形态。因此，₆₁ BM或PC ₇₁ BM）作为电子受体。在基于BDTy-2TVTDPP的单元中获得的最大功率转换效率为2.85％，是基于BDTx-2TVTDPP的单元的1.8倍。这项研究表明，改变BDT的取代位置可显着改善其生成的SM的光伏性能。