Geometry-Controlled Crystallization and Dielectric Screening for Low-Loss Fully Non-Fused Organic Photovoltaics

Fully non-fused-ring acceptors (FNRAs) have been regarded as promising alternatives for organic photovoltaic (OPV) cells, owing to their simplified synthesis, low cost, and structural versatility when compared with fused materials. However, their photovoltaic performance is still limited by insufficient solid-state order and pronounced energy losses. Herein, a geometry-optimized FNRA, GS-12, was developed to elucidate how molecular geometry governs crystallinity and energy loss in OPV cells. Despite sharing an identical conjugated framework with the structurally related analogue GS-ISO, GS-12 exhibits enhanced crystallinity, tighter π-π stacking, a higher dielectric constant, and reduced energetic disorder, which collectively facilitate efficient charge separation and balanced carrier transport. As a result, the PBQx-TF:GS-12 device delivers a power conversion efficiency of 11.0% with reduced nonradiative energy losses, markedly outperforming its GS-ISO counterpart. Furthermore, incorporation of GS-12 into the PBQx-TF:TBT-26 system boosts the efficiency to 18.1%, which is one of the highest reported values for FNRA-based ternary OPV cells.