Direct Visualization of Polarity‐Driven Carrier Redistribution in Two‐Dimensional In/CdS

The intrinsic polarization field (IPF) in wurtzite semiconductors has long been proposed as a means to regulate carrier migration in photocatalytic and optoelectronic systems. However, direct experimental visualization of polarity‐driven charge separation remains challenging because intrinsic polarization effects are often obscured by competing surface fields and structural heterogeneity, leading to long‐standing contradictions between theory and experiment. Here, we fabricate well‐defined two‐dimensional In‐doped CdS single‐crystalline flakes (In/CdS) with exposed polar basal planes, providing a model platform to directly probe polarity‐driven carrier redistribution. Kelvin probe force microscopy, combined with photo‐deposition and single‐molecule fluorescence imaging, reveals opposite carrier accumulation on the two basal surfaces of individual flakes, with the upper surface serving as an electron‐rich reduction site and the bottom surface acting as a hole‐rich oxidation site. The spatially separated carrier distribution enables selective co‐catalyst loading on electron‐accumulated surfaces and boosts photocatalytic H 2 evolution. Ultrafast spectroscopy reveals a long lifetime (>2 µs) of photogenerated electrons and ultrafast electron transfer to co‐catalysts with an efficiency approaching unity. This work provides long‐sought experimental proof of charge separation in polar semiconductors and establishes a paradigm for exploiting intrinsic bulk properties through 2D geometry.