Dramatically different photovoltaic effect induced by siloxane-terminated combinatory side chain in polymer solar cells

Combinatory side chains have attracted much attention for molecular engineering in recent years. In this work, siloxane-terminated alkylthiol thiophene as a new combinatory side chain was developed to construct a new wide band-gap polymer CY1. Interestingly, the polymer CY1 exhibited preferential compatibility with nonfullerene acceptor rather than with fullerene acceptor, as revealed by Flory-Huggins interaction factor. The power conversion efficiency of the device based on CY1:IDIC was much higher than that based on CY1:PC71BM even with the additive. The contrasting performance is mainly ascribed to the different morphology induced by siloxane-terminated combinatory side chain on the polymer backbone. Our preliminary result demonstrates that a suitable combinatory side chain should be valuable to tune the compatibility between polymer donor and nonfullerene acceptor and finally promote the photovoltaic performance.