Facet‐Dependent Charge Dynamics of 2D Butylammonium Lead Bromide Perovskite Single Crystals

2D halide perovskites such as BA ₂ PbBr ₄ exhibit highly anisotropic optoelectronic properties arising from their unique layered crystal structure. While most previous studies have focused on polycrystalline thin films, single‐crystal systems remain less explored, and the influence of crystallographic facet orientation on their electronic and ionic behavior is still not well understood. In this study, we systematically investigated the charge dynamics and electrostatic response of single‐crystal BA ₂ PbBr ₄ on both cross‐sectional and normal surfaces using Kelvin probe force microscopy (KPFM). Under different light illumination and bias voltage, the distinct variation in contact potential difference (CPD) reveals enhanced screening of positively charged bromine vacancies and stronger light‐induced tip‐induced band bending (TIBB) on cross‐section surfaces. Time‐dependent measurements show that ionic relaxation is slower; however, the relaxation of photoinduced charge is faster at cross‐section facets. These findings thus reveal intrinsic details of the anisotropic interplay of charge screening, ion migration, and trap states, which offer primary insight into single‐crystal 2D perovskite's facet‐dependent optical and electronic behavior. This understanding provides a foundation for rationally engineering facet orientation and defect chemistry to unlock the full potential of 2D perovskites in stable optoelectronic devices.