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 form 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 (R1 and R2) 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 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 (Pdiss = 99.60%). This study demonstrates the great potential of non-fused small-molecule CIMs with rationally designed side chains for developing high-performance OSCs.