Asymmetrical vs Symmetrical Selenophene-Annulated Fused Perylenediimide Acceptors for Efficient Non-Fullerene Polymer Solar Cells

Recently, more attention has been paid to the heterocycles of perylenediimide-based small-molecule acceptors (SMAs) in aiming to improve the efficiency of the corresponding non-fullerene polymer solar cells (NF-PSCs). Meanwhile, recent studies have revealed that asymmetric configuration could provide better photovoltaic performances than its symmetric configuration. Herein, we design and synthesize the asymmetric and symmetric fused perylenediimide dimer (FPDI)-based small-molecule acceptors (FPDI-Se and FPDI-2Se) by incorporating the selenophene heterocycle into the bay position of FPDI. The effect of this Se heterocycle in the optical and electrochemical properties are systematically studied and discussed. Interestingly, with PTB7-Th as the polymer donor, the symmetric annulated acceptor FPDI-2Se-based device only gave an inferior power conversion efficiency (PCE) of 4.45% with a poor fill factor (FF) of 39.5%, whereas the asymmetric annulated acceptor FPDI-Se-based device, however, showed the remarkable enhanced PCE of 6.61% with an increased short-circuit current density of 14.78 mA/cm² and an improved FF of 56.1% in NF-PSCs, which was attributed to the better intra- and intermolecular interactions of FPDI-Se compared with those of FPDI-2Se. These results indicate that the design and development of the heteroannulated-FPDI electron acceptors with asymmetrical configuration is an effective strategy by which to improve the photovoltaic performances of PSCs.