Terminal group engineering of A-DA'D-A non-fullerene acceptors as electron transport materials for efficient inverted perovskite solar cells.

Conventional fullerene-based electron transport materials (ETMs) suffer from limited tunability and suboptimal interfacial contact, hindering further efficiency improvements in inverted perovskite solar cells (PSCs). In this study, two non-fullerene small molecules with chlorinated thiophene terminal groups Cl24-TCl and difluorinated phenyl terminal groups Cl24-F were employed as ETMs in inverted PSCs to investigate the key factors by which different terminal groups influence device performance. Although the Cl24-TCl ETM exhibits a more polarized electrostatic potential distribution and a larger dipole moment, the Cl24-F ETM shows more favorable energy level alignment and interfacial contact, which effectively reduce interfacial charge recombination losses. In addition, Cl24-F displays more compact π-π stacking, resulting in higher electron mobility and conductivity, thereby promoting more efficient interfacial charge transport. Consequently, inverted PSCs based on Cl24-F achieve a champion efficiency of 24.18%, which is significantly higher than that of devices based on Cl24-TCl (13.02%). This work uncovers the key factors governing device performance and guides the design of high-performance non-fullerene ETMs.