External electric field-dependent photoinduced charge transfer in non-fullerene organic solar cells

Based on Marcus theory, the photoinduced electron transfer properties of D-A type non-fullerene acceptor organic solar cells (OSCs) under the dependence of external electric field (F_ext) were investigated. The research results shown that the charge transfer mode under different F_ext intensities changes with certain regularity. Focusing on the important parameters (ΔG, λ, and V_DA) that affect the charge transfer rate, it was found that both charge separation (|ΔG_CS|>λ(1.3019 vs 0.8275 eV at F_ext = 0) and charge recombiation (|ΔG_CR|>λ, (1.9633 vs 0.8275 eV)) processes occur in the Marcus inverted region. The ΔG_CS is relatively sensitive to F_ext, and the calculated ΔG_CS at different F_ext intensities yields an increment of 0.0073 eV, which is also the main reason for the increase in the rate of charge separation. The ΔG_CR ranges between -1.9633 and -1.9637 eV, is insensitive to F_ext, and ΔG_CR is significantly smaller than ΔG_CS, which makes the charge recombination rate significantly smaller than the charge separation rate. For V_DA, it is found that V_DA will transition to a new level only when the F_ext intensity reaches a certain intensity, which also enables to obtain a faster charge separation rate. By studying the charge transfer parameters in different polar solvents, it is found that polar solvents can indeed increase the charge transfer rate. To a certain extent, our results also demonstrate that the addition of F_ext can further improve the performance of non-fullerene acceptor OSCs.