A Facile Direct C-H Arylation Approach Enables Low-Band Gap Completely Non-Fused Ring Acceptors for High Efficiency Organic Solar Cells.

Developing environmentally benign and efficient non-fused ring electron acceptors (NFREAs) with simplified molecular structures and reduced synthetic complexities is a key objective for advancing OSC technology. In conventional NFREA synthesis, typically relies on Stille/Suzuki coupling, which suffers from poor atom economy, multiple steps, high cost, and environmental concerns. Herein, we report a series of A-D-A type fully NFREAs, namely SN-4, SN-5, and SN-6 were designed and synthesized in three steps via a direct C-H arylation strategy that avoids fused-ring construction and hazardous organotin reagents. These acceptors exhibit narrow optical bandgaps (∼1.44 eV) with strong near-infrared light absorption, enabling superior light-harvesting. Molecular dynamics simulations reveal pronounced terminal-terminal interactions, highlighting the pivotal role of end-group interactions in governing molecular packing. Among the series, the binary device based on PM6:SN-6 achieves a remarkable power conversion efficiency (PCE) of 15.86% under green-solvent processing, surpassing SN-4 (7.85%) and SN-5 (12.88%) owing to enhanced charge transport, low radiative energy losses, and reduced trap-assisted recombination. This work demonstrates a sustainable, efficient, and scalable pathway for developing low-cost, narrow-bandgap, high-performance NFREAs, and advancing their potential for future organic photovoltaic applications.