Structural Fusion Yields Guest Acceptors that Enable Ternary Organic Solar Cells with 18.77 % Efficiency

The design and selection of a suitable guest acceptor are particularly important for improving the photovoltaic performance of ternary organic solar cells (OSCs). Herein, we designed and successfully synthesized two asymmetric silicon–oxygen bridged guest acceptors, which featured distinct blue‐shifted absorption, upshifted lowest unoccupied molecular orbital energy levels, and larger dipole moments than symmetric silicon–oxygen‐bridged acceptor. Ternary devices with the incorporation of 14.2 wt % these two asymmetric guest acceptors exhibited excellent performance with power conversion efficiencies (PCEs) of 18.22 % and 18.77 %, respectively. Our success in precise control of material properties via structural fusion of five‐membered carbon linkages and six‐membered silicon–oxygen connection at the central electron‐donating core unit of fused‐ring electron acceptors can attract considerable attention and bring new vigor and vitality for developing new materials toward more efficient OSCs. Herein, the novel asymmetric guest acceptor was rationally designed by combining the structural fusion and unidirectional extension strategies. The optimized ternary device with the incorporation of this guest acceptor achieved considerably improved power conversion efficiency (PCE) of 18.77 % with a boosted open‐circuit voltage (Voc) of 0.896 V.