Subtle Side-Chain Engineering of Random Terpolymers for High-Performance Organic Solar Cells

Terpolymers comprising three different components in the backbone have emerged as a new design strategy for conjugated polymers. However, compared with the backbone modification, less effort has been devoted to the alkyl side chain engineering, especially the subtle side chain modifications of random polymers. In this contribution, we designed and synthesized a series of random terpolymers, in which the subtle side chain regioregularity is used to finely tune the optical, electronic, and morphological properties. PBS5 was found to outperform the other copolymers with better mixing with fullerene and higher photovoltaic performance. Moreover, the utilization of these random terpolymers in nonfullerene solar cells was investigated. A well-known nonfullerene acceptor, ITCPTC, was used as the acceptor. Among the terpolymers, PBSS yielded the best photovoltaic performance with an impressive PCE of 12.1%, representing the highest value reported in the literature so far for nonfullerene OSCs based on random terpolymers. This work demonstrates the importance of subtle side chain engineering of random terpolymers for high performance organic solar cells.