Incorporation of selenophene into thienoazacoronene-based nonfullerene acceptor: impact on photophysical and photovoltaic properties

Abstract The singlet exciton (S1) lifetime of nonfullerene acceptor (NFA) films is a crucial factor influencing their photovoltaic performances, as a longer S1 lifetime increases the exciton diffusion length. We previously reported that a NFA with a two-dimensionally π-extended thienoazacoronene (TAC) central core, S-TACIC, exhibits an exceptionally long S1 lifetime in the film. In this study, we examined the effects of replacing thiophene with selenophene on the photophysical and photovoltaic properties. Fluorescence decay measurements showed that the S1 lifetime of the selenophene-substituted TAC-based NFA (Se-TACIC) is longer in solution (500 ps) but significantly shorter in the film (<200 ps) compared to S-TACIC (220 ps in solution and 1,590 ps in film). When blended with the polymer donor PBDB-T, the Se-TACIC-based organic photovoltaic (OPV) device exhibited a lower power conversion efficiency (5.58%) than the S-TACIC-based one (9.92%), due to inferior photovoltaic parameters of the Se-TACIC-based OPV device.