Conformationally Locked Medium Bandgap Non-Fused Electron Acceptors via Direct C–H Arylation for Efficient Organic Solar Cells Using Non-Halogenated Solvent

The development of high-performance, fully non-fused ring electron acceptors (NFREAs) for organic solar cells (OSCs) is often hindered by multistep synthesis, use of hazardous reagents, and high synthetic complexity (SC), ultimately limiting their figure-of-merit (FOM). In this study, we report three simple and cost-effective NFREAs, SN-1, SN-2, and SN-3, featuring a dialkoxybenzene central core and hexyldicyanorhodanine terminal acceptor groups linked via distinct π-bridging units: furan, thiophene, and ethylenedioxythiophene (EDOT), respectively. These NFREAs were synthesized in just four steps using a direct C–H arylation reaction, without any hazardous reagents, with very high overall yields of up to 49%. To enhance the molecular planarity and charge transport, an intramolecular noncovalent interaction strategy was employed to restrict the C–C bond rotation between the π-conjugated units. Notably, SN-3 exhibited multiple O···S and O···H interactions between core and end groups, effectively rigidifying the backbone and promoting J-aggregation. As a result, PM-6:SN-3-based OSCs achieved a power conversion efficiency (PCE) of 11.56%, a high FOM of 67.09, and a low SC value of 17.26. In comparison, devices based on SN-1 and SN-2 delivered PCEs of 10.26% and 6.97%, respectively. These findings underscore the critical role of noncovalent interactions in conformationally stabilizing simple NFREAs and highlight their potential for high FOM OSCs.