Non‐Fully Conjugated Dimerized Giant Acceptors with Different Alkyl‐Linked Sites for Stable and 19.13 % Efficiency Organic Solar Cells

Abstract Achieving both high power conversion efficiency (PCE) and device stability is a major challenge for the practical development of organic solar cells (OSCs). Herein, three non‐fully conjugated dimerized giant acceptors (named 2Y‐sites, including wing‐site‐linked 2Y‐wing, core‐site‐linked 2Y‐core, and end‐site‐linked 2Y‐end) are developed. They share the similar monomer precursors but have different alkyl‐linked sites, offering the fine‐tuned molecular absorption, packing, glass transition temperature, and carrier mobility. Among their binary active layers, D18/2Y‐wing has better miscibility, leading to optimized morphology and more efficient charge transfer compared to D18/2Y‐core and D18/2Y‐end. Therefore, the D18/2Y‐wing‐based OSCs achieve a superior PCE of 17.73 %, attributed to enhanced photocurrent and fill factor. Furthermore, the D18/2Y‐wing‐based OSCs exhibit a balance of high PCE and improved stability, distinguishing them within the 2Y‐sites. Building on the success of 2Y‐wing in binary systems, we extend its application to ternary OSCs by pairing it with the near‐infrared absorbing D18/BS3TSe‐4F host. Thanks to the complementary absorption within 300–970 nm and further optimized morphology, ternary OSCs obtain a higher PCE of 19.13 %, setting a new efficiency benchmark for the dimer‐derived OSCs. This approach of alkyl‐linked site engineering for constructing dimerized giant acceptors presents a promising pathway to improve both PCE and stability of OSCs.