Aoshima Kenta, Ide Marina, Saeki Akinori
Department of Applied Chemistry, Graduate School of Engineering, Osaka University 2-1 Yamadaoka Suita Osaka 565-0871 Japan
Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST) 4-1-8 Honcho Kawaguchi Saitama 332-0012 Japan.
RSC Adv. 2018 Aug 28;8(53):30201-30206. doi: 10.1039/c8ra05903a. eCollection 2018 Aug 24.
Diketopyrrolopyrrole (DPP) is a representative electron acceptor incorporated into narrow-bandgap polymers for organic photovoltaic cells (OPV). Commonly, identical aromatic units are attached to the sides of the DPP unit, forming symmetric DPP polymers. Herein we report the synthesis and characterization of DPP copolymers consisting of unsymmetric configurations of the side aromatics. The unsymmetric DPP copolymer with thienothiophene and benzene side moieties exhibits good solubility owing to the twisted dihedral angle at benzene and regiorandom configuration. A significant shallowing of the highest occupied molecular orbital level is observed in accordance with the electron-donating nature of the side units (benzene, thiophene, and thienothiophene). The overall power conversion efficiencies of the unsymmetric DPPs (2.3-2.4%) are greater than that of the centrosymmetric analogue (0.45%), which is discussed in view of bulk heterojunction morphology, polymer crystallinity, and space-charge-limited current mobilities. This comparative study highlights the effect of unsymmetric design on the molecular stacking and OPV performance of DPP copolymers.
二酮吡咯并吡咯（DPP）是一种典型的电子受体，被引入用于有机光伏电池（OPV）的窄带隙聚合物中。通常，相同的芳族单元连接在DPP单元的两侧，形成对称的DPP聚合物。在此，我们报道了由侧链芳族化合物的不对称构型组成的DPP共聚物的合成与表征。具有噻吩并噻吩和苯侧基的不对称DPP共聚物由于苯处的扭曲二面角和区域无规构型而表现出良好的溶解性。根据侧链单元（苯、噻吩和噻吩并噻吩）的给电子性质，观察到最高占据分子轨道能级有显著变浅。不对称DPP的整体功率转换效率（2.3 - 2.4%）高于中心对称类似物（0.45%），这从本体异质结形态、聚合物结晶度和空间电荷限制电流迁移率的角度进行了讨论。这项比较研究突出了不对称设计对DPP共聚物分子堆积和OPV性能的影响。
