Electrostatic Modulation of Central Units Enables High-Performance Fused-Ring Trimeric Acceptors

Fused-ring trimeric acceptor benefits from both the high symmetry/planarity of small-molecule acceptors and the large glass transition temperature of polymeric acceptors, making it highly potential to achieve organic solar cells (OSCs) with excellent power conversion efficiencies (PCEs) and long-term stabilities simultaneously. However, due to the structural complexity of ring-fused trimeric acceptor, conveniently tuning its optoelectronic properties remains a significant challenge. Herein, the first family of optically and electrostatically tunable fused-ring trimeric acceptors (CH34, CH35, and CH36) is constructed by incorporating electron-donating triazatruxene, electron-neutral triphenylene and electron-withdrawing tricycloquinazoline as central planes, respectively. All the trimeric acceptors maintain the intrinsic rigidity and planarity of molecular skeleton, which endow them with very small reorganization energies and weak electron-phonon coupling. Moreover, the quite different electrostatic properties of central cores exert significant effects on the energy levels distribution and light harvesting capacity of acceptors. Consequently, CH36 achieves a good PCE of 16.73%, representing the best performance among ring-fused trimeric acceptors. Remarkably, CH36-based ternary OSCs further render an excellent PCE of 20.48% along with substantially improved operational stability. Our work demonstrates the great potential of fused-ring trimeric acceptor for realizing both highly efficient and stable organic photovoltaics.