Ultrafast Photoinduced Charge Separation in Quasi‐2D Perovskites Enables Enhanced Photocurrent Generation

ABSTRACT Quasi‐two‐dimensional (quasi‐2D) metal halide perovskites exhibit rich phase heterogeneity that profoundly influences light‐matter interactions and charge transport. However, the fundamental mechanisms governing carrier transfer across distinct phases remain poorly understood. Here, we demonstrate effective electron–hole separation in fluorinated multilayered (4‐FBA) 2 (MA) n‐1 Pb n I 3n+1 films nominally prepared with n = 3, using femtosecond transient absorption (TA) spectroscopy. The films display a heterogeneous distribution of phases naturally stacked along the growth direction. Ultraviolet photoelectron spectroscopy measurements, supported by density functional theory calculations, reveal a type‐II band alignment between the small‐n phases and the bulk perovskite. This staggered alignment drives charge separation through both direct and sequential carrier transfer mechanisms, wherein electrons preferentially migrate into the bulk domains while holes accumulate in the small‐n layers. The nearly symmetric transfer times of electrons and holes yield an efficient and balanced spatial separation of carriers. Global target analysis of TA data quantitatively reproduces the spectral evolution, providing a rigorous validation of the mechanism. Furthermore, diode devices fabricated from (4‐FBA) 2 (MA) n‐1 Pb n I 3n+1 exhibit pronounced photocurrent enhancement, consistent with efficient bidirectional photocarrier transfer. This study provides a comprehensive understanding of interphase charge transfer in fluorinated quasi‐2D perovskites and highlights strategies to engineer directional separation pathways for high‐performance photovoltaic, optoelectronic, and quantum devices.