Crystallization Kinetic Control of Non‐Fused Ring Electron Acceptors via Asymmetric Molecular Engineering for High‐Efficiency Organic Solar Cells

ABSTRACT Controlling the aggregation behavior and crystallization kinetics of non‐fused‐ring electron acceptors (NFREAs) is essential for optimizing the active‐layer morphology of organic solar cells (OSCs). Here, an asymmetric NFREA, XY‐NF‐4Cl, is developed by integrating bis(4‐ethylphenyl) and 2‐(2,6‐dibutoxy‐4‐fluorophenyl) side chains into one molecular framework, with two symmetric analogs as controls. Compared with the symmetric counterparts, XY‐NF‐4Cl exhibits improved solubility and donor–acceptor miscibility, which slows film solidification and allows more sufficient molecular reorganization during film formation. Consequently, the blend film forms a well‐defined fibrous interpenetrating network and a predominantly face‐on orientation. This favorable morphology promotes balanced charge‐transport and suppresses charge recombination, enabling a power conversion efficiency of 17.86%, significantly higher than that of the symmetric counterparts. This work demonstrates that asymmetric side‐chain engineering is an effective strategy for regulating crystallization kinetics and morphology evolution in NFREA‐based OSCs.