3‐Benzofuranone Based Asymmetric Guest Nonfullerene Acceptors for Reduced Voltage Loss

ABSTRACT Finding solutions that enable improvements in efficiency while enhancing stability remains a major challenge in the field of organic solar cells. In this paper, we select 3‐benzofuranone and its monofluorinated derivatives, namely 5‐fluoro‐3‐benzofuranone and 6‐fluorobenzofurane‐3(2H)‐one, as luminescent end groups and synthesize three asymmetric nonfullerene acceptors, denoted as ZHY1, ZHY2, and ZHY3, respectively. Addition of a small amount of ZHY1, ZHY2, or ZHY3 (0.03 in wt/wt) as the guest component in PM6:BTP‐eC9 reduces the ππ‐stacking distance and increases crystalline correlation length of both the PM6 and BTP‐eC9 phases, hence accelerates charge separation, prolongates exciton lifetime, reduces non‐radiative energy loss, increases charge mobilities, improves charge extraction and collection efficiency, and suppresses both monomolecular and bimolecular recombination, giving rise to a simultaneous photovoltaic performance and device stability. The host binary device and the ZHY3‐based ternary device exhibit power conversion efficiencies of 18.3% and 19.5%, respectively. These results indicate that 3‐benzofuranone and its derivatives are promising building blocks for designing asymmetrical nonfullerene acceptors towards high‐efficiency photovoltaic materials.