High-efficiency organic solar cells enabled by non-ionic small-molecule cathode interlayers with tunable alkoxy side chains

Abstract

Interfacial engineering plays a critical role in enhancing the performance of organic solar cells (OSCs). We report herein two novel alcohol-soluble small-molecule cathode interlayer materials (CIMs), M-dOR and M-tOR, featuring a non-fused donor–acceptor architecture. These molecules are constructed from a 1,3-dibromobenzene core conjugated to cyclopentadithiophene (CPDT) donor arms via direct C–H arylation, and terminated with rhodanine acceptors. By introducing alkoxy groups with different lengths through side-chain engineering, the solubility and interfacial properties are allowed to modulate, providing excellent processability in alcoholic solvents and superior device performance for the target materials. When employed as a cathode interlayer in PM6:Y6-based OSCs, M-tOR achieves a champion power conversion efficiency (PCE) of 15.36%, outperforming the 15.12% efficiency of the benchmark PDINO. The enhanced performance originates from the synergistic effects of optimized energy level alignment, improved film morphology, higher electron mobility (4.47 × 10⁻⁴ cm² V⁻¹ s⁻¹), and efficient exciton dissociation (P_diss = 99.60%). This study demonstrates the great potential of non-fused small-molecule CIMs with rationally designed side chains for developing high-performance OSCs.