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

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.