Deciphering the effect of chalcogen-incorporated heterocycles in nonfused electron acceptors for organic photovoltaics

Two simple nonfused electron acceptors, 2T2TT-F and 2T2SeT-F, are developed via incorporating thieno[3,2-b]thiophene and selenopheno[3,2-b]thiophene as π-conjugated linkers, respectively. Both of them display similar absorption spectra, whereas 2T2SeT-F possesses higher crystallinity than 2T2TT-F. When combined with polymer donor PM6, organic solar cells based on 2T2TT-F have obtained a higher power conversion efficiency (PCE) of 11.31% than 2T2SeT-F-based solar cells (8.47%). It is due to the high-rising energy levels, and the suitable crystallinity and miscibility of the blend film, and thus optimal phase separation to suppress charge recombination for 2T2TT-F. These results reveal new insights that chalcogen-heterocycle substituents play dramatic roles in governing the molecular properties and photovoltaic performance of non-fused electron acceptors.