A-π-D-π-A type conjugated small molecule plays an indispensable role in organic photovoltaics. Understanding the relationship between the molecular structure and performance is a fundamental question for further rational design of high performance organic materials. To red-shift the absorption spectrum of benzo[1,2-b:4,5-b']dithiophene (BDT) based A-π-D-π-A type compounds, electron donating 3,4-ethylenedioxythiophene (EDOT) moiety was introduced into the π-conjugation bridge unit. Two new compounds that having EDOT next to the central BDT core (COOP-2HT-EDOT-BDT) or next to the terminal electron acceptor unit (COOP-EDOT-2HT-BDT) were synthesized and characterized. The compound COOP-2HT-EDOT-BDT showed higher molar extinction coefficient (εabsmax = 1.06 × 105 L mol-1 cm-1), lower optical band gap (Eg = 1.56 eV) and high HOMO energy level (EHOMO = -5.08 eV) than COOP-EDOT-2HT-BDT (εabsmax = 0.96 × 105 L mol-1 cm-1, Eg = 1.71 eV, EHOMO = -5.26 eV), which is attributed to the intensive interaction between the EDOT unit and the HOMO orbital, as confirmed by the theoretical calculation results. However, higher power conversion efficiency of 3.58% was achieved for the COOP-EDOT-2HT-BDT:PC61BM based solar cells, demonstrating that the electron donating EDOT unit adjacent to the electron-withdrawing end-capped group (COOP) is a better way to achieve high performance photovoltaic materials.

中文翻译：

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A-π-D-π-A型共轭分子中给电子3,4-亚乙基二氧噻吩（EDOT）部分的位置对光电性能和光电性能的影响

A-π-D-π-A型共轭小分子在有机光伏中起着不可或缺的作用。了解分子结构与性能之间的关系是高性能有机材料进一步合理设计的基本问题。为了使基于苯并[1,2-b：4,5-b']二噻吩（BDT）的A-π-D-π-A型化合物的吸收光谱发生红移，给电子3,4-亚乙基二氧噻吩（EDOT）部分被引入到π-共轭桥单元中。合成并表征了两种新化合物，它们的特征是：EDOT紧靠中心BDT核（COOP-2HT-EDOT-BDT）或紧靠末端电子受体单元（COOP-EDOT-2HT-BDT）。化合物COOP-2HT-EDOT-BDT的摩尔消光系数较高（εabsmax= 1.06×105 L mol-1 cm-1），光学带隙较低（Eg = 1）。56 eV）和比COOP-EDOT-2HT-BDT高的HOMO能级（EHOMO = -5.08 eV）（εabsmax= 0.96×105 L mol-1 cm-1，Eg = 1.71 eV，EHOMO = -5.26 eV），理论计算结果证实，这归因于EDOT单元与HOMO轨道之间的强烈相互作用。然而，基于COOP-EDOT-2HT-BDT：PC61BM的太阳能电池实现了3.58％的更高功率转换效率，表明与吸电子封端基团（COOP）相邻的给电子EDOT单元是一种更好的方法实现高性能的光伏材料。