Molecular Structure-Dependent External Electric Field Modulation of Interfacial Charge Separation

Based on density functional theory, this paper systematically investigates the external electric field-regulated charge-transfer behavior of two donor:acceptor interfaces, PBDB-T:CF3-BDP-Cz and PBDB-T:CF3-BDP-TPA. These two BODIPY-based acceptors share the same BODIPY core but differ in their terminal donor groups, namely carbazole (Cz) and triphenylamine (TPA), providing a well-defined model system for elucidating the relationship between molecular structure and interfacial charge transfer. The results show that the different terminal groups lead to significant differences in the electric-field response mechanisms of the two interfaces. For the PBDB-T:CF3-BDP-Cz interface, the excited-state properties show a relatively weak response to the electric field, while the charge-transfer rate exhibits a nonmonotonic dependence on electric-field intensity, and an optimal electric-field range is identified that favors charge separation. The charge-transfer characteristics of the PBDB-T:CF3-BDP-TPA interface are more sensitive to changes in the electric field. Although the charge-recombination rate is consistently higher than the charge-separation rate throughout the entire electric-field range, the relative efficiency of charge separation continuously increases with increasing electric-field strength because the charge-separation rate increases more rapidly than the charge-recombination rate. This study reveals the intrinsic relationship between terminal-group structure, electric-field modulation, and interfacial charge-transfer mechanism, providing a theoretical basis for understanding the field-controlled charge-separation mechanism of organic photovoltaic interfaces.