Brush‐Like Tetrameric Acceptors Achieving over 20% Efficiency With Exceptional Stability and Mechanical Robustness

Well-defined high-molecular-weight acceptors have recently emerged as promising materials for organic solar cells (OSCs), offering high power conversion efficiency (PCE), long-term stability, and intrinsic stretchability. However, the limited synthetic accessibility of these materials hampers their large-scale application. Herein, we propose an efficient "brush-like" synthetic strategy to construct high-molecular-weight acceptors (diYCl, teYCl, and pYCl) with precisely controlled molecular structures. Our results reveal that the well-defined molecular architecture and enlarged molecular sizes effectively suppress molecular diffusion, thereby improving thermodynamic stability. Among them, teYCl achieves the optimal balance between efficiency and stability, affording a PCE of 18.02% in D18/teYCl-based quasiplanar heterojunction (Q-PHJ) OSCs. The device also exhibits remarkable operational durability, with T₈₀ lifetimes of 5000 h at 65°C and 61 600 h under dark storage. Moreover, when teYCl is employed as a coacceptor in Q-PHJ architectures, the PCE further rises to 20.19%, representing the highest efficiency reported for such bilayer-dominated Q-PHJ devices. The enlarged molecular size also endows the OSCs with enhanced mechanical robustness, with teYCl- and pYCl-based stretchable devices maintaining 80% of their initial PCEs at 31% and 40% strain, respectively. This study offers a practical molecular design strategy for developing high-efficiency, stable, and intrinsically stretchable acceptors toward next-generation OSCs.