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

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. Two donor-acceptor-substituted coumarin-based molecules with distinct molecular packing are developed showing impressive power conversion efficiencies up to 15.34% in ternary organic solar cells by fine tuning the optoelectronic properties and the use of complementary absorbing molecular acceptors.image & COPY; 2023 WILEY-VCH GmbH