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.

提升构象稳定性并调控分子组装行为，是开发高效低成本非稠环电子受体（nonfused ring electron acceptors，NFREAs）的核心需求。大位阻侧链可有效限制碳-碳（C-C）单键的自由旋转，但这类侧链在结构多样性与合成可及性方面仍存在局限，为材料成本的进一步优化留有空间。本文通过合理设计环己基衍生的大位阻侧链，报道了两种非稠环电子受体（UF-CHex-2F与UF-CHexC3-2F）。环己基体本征稳定的椅式构象可提供空间位阻，同时抑制侧链无序化。这种环己基构象锁定策略能够稳定分子主链并调控分子组装行为。因此，基于PBQx-TF:UF-CHexC3-2F的共混薄膜形成了有序堆叠结构与纳米级相分离形貌，可促进高效的激子扩散与电荷传输。对应的器件获得了15.42%的高功率转换效率（power conversion efficiency，PCE），证实了通过简单大位阻侧链策略可满足有机太阳能电池（organic solar cells，OSCs）的商业化应用要求。