Cyclohexyl Conformational Locking Strategy: Molecular Assembly Engineering in Nonfused Acceptors for High-Efficiency Organic Solar Cells

Improving the conformational stability and regulating molecular assembly behavior are essential for developing high-efficiency and low-cost nonfused ring electron acceptors (NFREAs). Bulky side chains offer an effective approach to restrict the free rotation of carbon–carbon (C–C) single bonds but remain limited in structural diversity and synthetic accessibility, leaving room for further optimization of material costs. Herein, we report two NFREAs (UF-CHex-2F and UF-CHexC3-2F) through the rational design of cyclohexyl-derived bulky side chains. The intrinsically stable chair conformation of cyclohexyl furnishes steric hindrance while preventing side-chain disorder. This cyclohexyl conformational locking strategy stabilizes the backbone and regulates molecular assembly behaviors. Consequently, the PBQx-TF:UF-CHexC3–2F based blend film forms an ordered stacking property and nanoscale phase separation morphology, facilitating efficient exciton diffusion and charge transport. The corresponding devices obtained a high power conversion efficiency (PCE) of 15.42%, demonstrating the valuable insight into simple bulky side chains to meet the commercial application requirements of OSCs.