Backbone regulation of a bithiazole-based wide bandgap polymer donor by introducing thiophene bridges towards efficient polymer solar cells

Abstract Miscibility and morphology of the active layers have significant influence on the photovoltaic performance of polymer solar cells (PSCs). Chemical strategies, especially molecular structure design, have been proven to be crucial for polymer donor materials. In this work, two wide bandgap D-A copolymer donors composed of tripropylsilyl substituted bithienyl-benzodithiophene as donor (D) unit and dialkyl substituted bithiazole as acceptor (A) unit were designed and synthesized. By introducing thiophene π-bridges into the backbone, the miscibility and morphological properties of the materials are effectively tuned, leading to tremendous progress in power conversion efficiency from 0.95% to 10.73% with m-ITIC as the acceptor. The results demonstrate that manipulating molecular distortion can be an effective strategy to regulate molecular self-assembly behavior of the polymer donors and achieve excellent aggregation properties, blend miscibility, and photovoltaic performance of the PSCs.