Chemoselective synthesis of fluoroacetonitrile-containing terminal groups for stable non-fullerene acceptors.

The intrinsic instability of non-fullerene acceptors (NFAs), primarily caused by vulnerable exocyclic vinyl linkages, significantly undermines the operational lifetime of organic solar cells (OSCs). In this work, we address this challenge by designing robust molecular framework that incorporates fluoroacetonitrile-containing terminal groups. This terminal group enables the formation of a F···H interaction between itself and the exocyclic vinyl linkage. Leveraging this F···H interaction, we can readily synthesize the preferable E isomer with exclusive regioselectivity. Moreover, the F···H interaction locks the molecular conformation, resulting in a more planar structure, and thereby enhancing molecular packing and film morphology. Critically, this interaction stabilizes the exocyclic vinyl linkage, significantly boosting the chemical and photo-stability and suppressing terminal-group redistribution of the NFAs. When paired with the low-cost polymer donor P3HT, the symmetric acceptor E-2IFC-F achieves a power conversion efficiency (PCE) of 11.77%, setting a high benchmark for P3HT-based OSCs. Furthermore, the asymmetric acceptor E-IFC-IC-Cl, with its optimized energy levels, delivers a PCE of 19.31% when combined with the donor PM6. All of the devices based on these NFAs exhibit better stability. This work presents a paradigm for developing high-efficiency, stable, and low-cost OSCs, highlighting the potential of fluoroacetonitrile-containing terminal groups in enhancing NFA performance.