A comparative study on the thermal- and microwave-assisted Stille coupling polymerization of a benzodithiophene-based donor–acceptor polymer (PTB7)

Abstract

We report a comparative study on the thermal- and microwave-assisted Stille-coupling polymerization of a benzodithiophene-based donor–acceptor polymer (PTB7). For this study, we synthesized PTB7 polymers through Stille-coupling polymerization under microwave conditions (M-PTB7, M_n = 75 kg mol⁻¹, and D = 2.2) as well as thermal conditions (T-PTB7, M_n = 31 kg mol⁻¹, D = 2.1). Although the microwave-assisted method increases the molecular weight of PTB7 in a short time, the power conversion efficiency of M-PTB7 (2.8%) is lower than that of T-PTB7 (7.8%). The microwave-assisted method was found to generate more structural defects from homo-coupling side reactions, resulting in a decrease in J_SC and FF values for M-PTB7. Our findings highlight the importance of controlling the generation of homocoupled units during the synthesis of PTB7 polymers for high-performance PSCs.