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

ABSTRACT 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 T 80 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.