Structurally Complementary Star-Shaped Unfused Ring Electron Acceptors with Simultaneously Enhanced Device Parameters for Ternary Organic Solar Cells

Ternary strategy has attracted extensive attention for bulk heterojunction organic solar cells (BHJ OSCs) owing to their potentially improved light harvesting, cascaded energy levels, and optimized film morphology of binary BHJs. Herein, three novel star-shaped unfused ring electron acceptors (SSUFREAs), i.e., H1-3, with and without fluorine-substituent in phenyl core or peripheral group are designed and synthesized as third components via direct C-H arylation to incorporate into PM6:Y6 BHJ films. The structure-property-performance dependence study reveals that the isotropic charge transfer, complementary star-shape structure and light absorption, and energy-level cascades of H1-3 with PM6 and Y6 allow ternary BHJs to have higher power conversion efficiency (PCE) compared to the PM6:Y6 binary BHJ. Among them, the ternary BHJ involving fluorine-free H1, i.e., H1:PM6:Y6, possesses the highest PCE (16.57%) owing to the high-lying frontier molecular orbital and the enlarged torsion angle, which enhances open-circuit voltage, inhibits the excessive crystallization of Y6, and facilitates exciton dissociation as well as collection. The findings indicate that SSUFREAs have great potential to serve as third components to optimize morphology and improve the open-circuit voltage of BHJ OSCs.