Modulated Interactions Induced by Cyano-Modified Wide-Bandgap Small-Molecule Acceptors Enables High-Performance Ternary Organic Photovoltaics.

The cyano group is extensively employed in the molecular engineering of high-performance small-molecule acceptors (SMAs) for organic solar cells (OSCs) to fine-tune energy levels and optimize molecular packing. To date, the application of cyano group has predominantly been confined to end-group modification in SMAs, with limited investigation in central unit engineering. Herein, in this work, the role of cyano substitution is systematically investigated in the central unit of SMAs and design a novel cyano-functionalized wide-bandgap acceptor UF-BCN. The introduction of the cyano group significantly enhances the surface energy of the molecule and substantially deepens the highest occupied molecular orbital (HOMO) energy level due to its strong electron-withdrawing capability, then leading to a blue-shifted absorption. When introduced as the third component in the D18:BTP-eC9, UF-BCN demonstrates complementary light absorption, strong intermolecular interactions, and excellent compatibility with BTP-eC9 to form a mixed acceptor phase, enabling it to function as an effective morphological modulator within the ternary system. Consequently, the ternary OSC based on D18:BTP-eC9:UF-BCN achieves an impressive power conversion efficiency (PCE) of 19.34%. This study underscores the effectiveness of cyano substitution in central unit engineering and highlights its potential for optimizing active layer morphology and enhancing the performance of ternary OSCs.