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

“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.