Theoretical Study of Non-Fullerene Acceptors Using End-Capped Groups with Different Electron-Withdrawing Abilities toward Efficient Organic Solar Cells

Acceptors in organic solar cells (OSCs) are of paramount importance. On the basis of the well-known non-fullerene acceptor Y6, six acceptors (Y6-COH, Y6-COOH, Y6-CN, Y6-SO₂H, Y6-CF₃, and Y6-NO₂) were designed by end-capped manipulation. The effects of end-capped engineering on electronic properties, optical properties, and interfacial charge-transfer states were systematically studied by density functional theory, time-dependent density functional theory, and molecular dynamics. The designed acceptors possess suitable energy levels and improved optical properties. More importantly, the electron mobility of the new acceptors was greatly enhanced, even more than 20 times that of the parent molecule. Among them, Y6-NO₂ with the lowest-lying frontier molecular orbitals and the largest red-shifted absorption was selected to construct interfaces with the donor PM6. PM6/Y6-NO₂ exhibits stronger interfacial interactions and enhanced charge-transfer characteristics compared with PM6/Y6. This work not only enhances the understanding of the structure-property relationship for acceptors but also offers a set of promising acceptors for high-performance OSCs.