Cyanobenzene‐Modified Quinoxaline‐Based Acceptors with Optimal Excitonic Behavior Enable Efficient Organic Solar Cells

Abstract Cyanogroup (‐CN) is a strongly electron‐withdrawing and highly polar functional group; therefore, cyanation has been extensively utilized to optimize the terminal groups of high‐performance small‐molecule acceptors (SMAs) in organic solar cells (OSCs). Herein, by regulating the cyanobenzene substitution in the central core for the first time, four novel SMAs are synthesized, named phCN‐F, phCN‐Cl, 2phCN‐F, and 2phCN‐Cl. Theoretical and experimental analyses have shown that asymmetric and symmetric cyanobenzene‐substitution of the central core, coupled with selective terminal groups, can significantly affect the intrinsic excitonic properties of the molecule. Blends based on asymmetric cyanobenzene‐substitution molecules possess tighter molecular packing and more suitable phase separation to facilitate exciton dissociation, charge transport, and charge extraction. The optimal device performance of the phCN‐F‐based OSC reaches 20.16%, which is significantly higher than that of symmetrically substituted OSCs. Furthermore, devices prepared based on phCN‐F maintain over 90% of their initial efficiency after being heated at 85°C for 3000 h, demonstrating excellent thermal stability. This study elucidates the potential mechanisms for optimizing device performance through asymmetric cyanobenzene‐substitution of the central core, providing valuable insights for the further design of record‐breaking SMAs.