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

Abstract 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.