Photoinduced Charge Transfer at the D/A Interfaces of Isomerized DSMAs Regulated through an External Electric Field

Developing novel organic photovoltaic materials for organic solar cells (OSCs) requires precise characterization of their charge transfer states to optimize the photoinduced charge transfer mechanisms within the photoactive layer. The microscopic photoelectric properties of the S-shaped (DYA-I-S) and O-shaped (DYA-I-O) conformations of dimeric small molecule acceptors (DSMAs) are analyzed through density functional theory (DFT) calculations. The results indicated that the S-shaped conformation of DSMA exhibits significant advantages in planarity, energy gap, reorganization energy (λ), spectral red shift, and oscillator strength (f). Furthermore, D18 is used as a donor to construct the heterojunction interface, and the D18/DYA-I-S interface exhibited charge transfer states originating from different excitation sites. Using Marcus theory, we also explore the influence of the external electric field (F_ext) on the photoinduced charge transfer properties of the D18/DSMAs parallel-stacking interfaces. Notably, the D18/DYA-I-S interface exhibits a higher charge separation rate (k_CS), with F_ext exerting a more pronounced influence on its k_CS. This study reveals the impact of molecular conformational isomerization and F_ext modulation on the photoinduced charge transfer process, providing valuable insights for optimizing the OSCs performance.