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 (Fext) were investigated. The research results shown that the charge transfer mode under different Fext intensities changes with certain regularity. Focusing on the important parameters (ΔG, λ, and VDA) that affect the charge transfer rate, it was found that both charge separation (|ΔGCS|>λ(1.3019 vs 0.8275 eV at Fext = 0) and charge recombiation (|ΔGCR|>λ, (1.9633 vs 0.8275 eV)) processes occur in the Marcus inverted region. The ΔGCS is relatively sensitive to Fext, and the calculated ΔGCS at different Fext intensities yields an increment of 0.0073 eV, which is also the main reason for the increase in the rate of charge separation. The ΔGCR ranges between -1.9633 and -1.9637 eV, is insensitive to Fext, and ΔGCR is significantly smaller than ΔGCS, which makes the charge recombination rate significantly smaller than the charge separation rate. For VDA, it is found that VDA will transition to a new level only when the Fext 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 Fext can further improve the performance of non-fullerene acceptor OSCs.