Regulation of organic solar cells performance through external electric field: From charge transfer mechanisms to photovoltaic properties

In organic solar cells (OSCs), comprehending the charge transfer mechanism at D/A interfaces is crucial for photoinduced charge generation and enhancing power conversion efficiency (PCE). The charge transfer mechanism and photovoltaic performance of the parallel stacking interface configuration of the PTQ10 polymer donor and T2EH non-fullerene acceptor (NFA) are systematically studied at the microscopic scale. The analysis of the electron-hole distribution of the PTQ10/T2EH excited states revealed the presence of multiple charge excitation modes and charge transfer pathways. Using Marcus theory, we examine the charge separation rate (K_CS) of PTQ10/T2EH under external electric field (F_ext) modulation, and it is clarified that reorganization energy (λ) is the main factor that affects the K_CS. Our results show that F_ext has a positive impact on the photovoltaic properties of PTQ10/T2EH thin films, as evidenced by the modulation of the open circuit voltage (V_OC), voltage loss (V_LOSS) and fill factor (FF). Overall, this study provides valuable theoretical insights for F_ext to accelerate the charge separation process and enhance photovoltaic efficiency.