Asymmetric Alkyl Chain Engineering for Efficient and Eco-Friendly Organic Photovoltaic Cells.

Recent advancements in organic photovoltaic (OPV) cells have resulted in power conversion efficiencies (PCEs) surpassing 20%. However, the use of halogen solvents in the fabrication of OPV cells raises concerns due to their potential environmental and health impacts. In this work, a novel non-fullerene small molecule acceptor BO-AM-4F, featuring an asymmetric alkyl chain design that includes a 2-butyloctyl and a unique 6-(hexylamino)-6-oxohexyl chain is synthesized. This design significantly improves molecular packing, crystallinity, and electrostatic potential distribution compared to the controlled acceptor DBO-4F, which possesses symmetric 2-butyloctyl chains. When combined with the polymer donor PBDB-TF and processed using the non-halogen solvent o-xylene, the BO-AM-4F-based OPV cell achieves an impressive PCE of 18.0%, surpassing the 16.6% PCE observed in the PBDB-TF:DBO-4F device. Furthermore, the PBDB-TF:BO-AM-4F system demonstrates enhanced photostability and thermal stability compared to its DBO-4F counterpart. These findings emphasize asymmetric alkyl chain engineering as an effective strategy for developing high-performance, environmentally friendly OPV materials. This represents a significant step towards sustainable OPV technology.