Synergistic effect of benzoselenadiazole core and alkoxy side chain substitution on the photovoltaic performance of non-fullerene acceptors

Abstract

“Y-series” small-molecule acceptors (SMAs) have attracted extensive research interest as they boost the power conversion efficiencies of organic solar cells (OSCs) and research communities have begun to concentrate on the structure–property relationship and further structural optimization of this “A–DA′D–A” type SMA. In this study, we developed a novel Y-series SMA, called Y6–Se–O, by adopting benzoselenadiazole as the central core and alkoxy side chains on the β-position of thiophene moieties. The alkoxy substitution yields obvious effects on frontier orbitals of molecules and thus open-circuit voltage (V_OC) of the corresponding devices. The lowest unoccupied molecular orbital (LUMO) level of Y6–Se–O is up-shifted compared to that of Y6–Se, therefore, a higher V_OC of 0.94 V was attained. Additionally, when mixed with the donor polymer PM6, the Y6–Se–O-based blend films can maintain optimal morphology with stronger crystallinity and reasonable phase segregation, which leads to efficient charge dissociation, suppressed recombination, and balanced charge transportation. As a result, the PM6:Y6–Se–O-based devices reached a better efficiency of 17.5%. Our study demonstrated that the introduction of alkoxy side chains is an effective approach to tuning the optoelectrical properties of SMAs and facilitates both V_OC and efficiencies.