1,2,4‐Benzotriazine‐Based Asymmetric Acceptors with Dual π‐Conjugation Extension Achieve 20.74% Efficiency in Organic Solar Cells

Core‐asymmetric acceptors, which combine the advantages of electron‐deficient cores and molecular asymmetry, represent a promising yet underexplored design strategy for organic solar cells. Herein, we designed and synthesized two asymmetric 1,2,4‐benzotriazine‐based acceptors, H‐Th and H‐Th‐FN, both featuring a chlorinated thiophene unit side‐grafted onto the central core. The electron‐rich thiophene modulates the strong electron deficiency of the triazine core, while effective orbital overlap enhances molecular rigidity. Notably, H‐Th‐FN incorporates a fluoronaphthalene terminal to achieve dual π‐conjugation extension in the central core and end group, thereby affording a narrower bandgap and weaker electron‐phonon coupling. This structural strategy optimizes intermolecular packing, suppresses aggregation‐caused quenching, and reduces non‐radiative recombination loss to as low as 0.213 eV. As a result, the PM6:H‐Th‐FN binary device achieves a power conversion efficiency of 19.67%, while the corresponding ternary device achieves an impressive efficiency of 20.74%. This work develops a family of 1,2,4‐benzotriazine‐based acceptors for high‐performance organic solar cells, underscoring the advantages of central‐core asymmetry and its broad potential.