Tailoring the photovoltaic performance of benzothiadiazole-based D–A-type polymers by incorporating robust electron-withdrawing substituents

Abstract

The incorporation of electron-withdrawing substituents is one of the promising approaches to enhance the photovoltaic characteristics of p-type polymer donors. In this study, three benzothiadiazole (BT)-based D–A-type conjugated polymers decorated with different electron-withdrawing substituents were synthesized to understand the optimum constitution. First, a fluorinated alkylthienyl-substituted benzodithiophene donor was coupled with the BT acceptor via an alkylated thiophene bridge to yield the PB-BT reference. Subsequently, PB-BT was structurally modified by introducing strong electron-withdrawing F and CN units at the 5-position of the BT acceptor to afford two target polymers, PB-BTF and PB-BTCN, respectively. The optical, electrochemical, and photovoltaic properties of the three polymers were strongly dependent on the electron-withdrawing substituents. Notably, the polymer solar cell based on PB-BTF adopting the nonfullerene acceptor exhibited the highest power conversion efficiency (PCE) of 11.12 %, while those based on PB-BT and PB-BTCN exhibited PCEs of 9.56 % and 5.07 %, respectively. These results indicate that the choice of appropriate electron-withdrawing substituents is of great importance for developing high-performance BT-based D–A-type polymers.