Correlation of Functional Coumarin Dye Structure with Molecular Packing and Organic Solar Cells Performance

Abstract

Nowadays, ternary organic solar cells (OSCs) based on all‐small molecules have the convenient strategy toward high‐performance and stable devices. Herein, two coumarin‐based dyes C4 and C4–CN are designed and synthesized with a simple synthetic route. The molecules display different intra‐ and intermolecular interactions in the solid state originating from acceptor substitution, as revealed by the single‐crystal structure analysis. The introduction of dicyanomethylene acceptor group in C4–CN plays a synergistic role in molecular packing and orientation in the solid state, thus fostering the elongation of exciton lifetime and improved charge transport in photoactive layer. The optimized C4–CN:AQx–3‐based binary OSCs show a power conversion efficiency (PCE) of 15.07%, which is appreciably higher than the C4:AQx–3‐based OSC (11.39%) due to the appropriate energy‐level alignment, balanced charge transport, favorable phase separation, and lower charge recombination. Furthermore, by introduction of C4–CN as the third component into C4:AQx–3 blend, the ternary OSC shows an improved PCE of 15.34%, which is linked with the enhanced crystallization, optimized morphology, balanced charge carrier mobility, and suppressed recombination with low energy loss.