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.