Dynamic Feedback of Interfacial Electric Fields Governs Charge Extraction in Perovskite Solar Cells

Interfacial charge extraction is the kinetic bottleneck governing the open‐circuit voltage ( V OC ) in perovskite solar cells (PSCs), yet it is conventionally modeled as a static process characterized by a constant extraction velocity. Here, we demonstrate that interfacial extraction is inherently dynamic and self‐limiting, driven by a negative feedback loop where accumulating charges generate a transient electric field that suppresses subsequent carrier transfer. Using interface‐sensitive transient reflectance (TR) spectroscopy combined with a field‐modified diffusion‐extraction model, we resolve the time‐dependent extraction velocity, S F ( t ), at ITO/perovskite and ITO/SAM/perovskite buried interfaces. We uncover a fundamental trade‐off: efficient interfaces (e.g., SAM‐functionalized) exhibit high initial extraction rates ( S 0 ) but suffer from rapid field saturation (short τ ), leading to a sharp decay in extraction efficacy. This self‐generated field mechanism is corroborated by Kelvin probe force microscopy and explains the performance disparity in operational devices. To quantify this dynamic behavior, we introduce the time‐integrated extraction capacity, , as a robust descriptor of sustained performance. This metric accurately reflects the superior V OC (1.18 V versus 1.13 V) and efficiency (26.47% versus 25.45%) of optimized SAM‐based devices, establishing a new paradigm for designing interfaces that minimize field‐induced losses.