Illumination‐Dependent Photoelectric Anisotropy in Cs₃Bi₂I₉ Single Crystal Sheets

Abstract Lead‐free all‐inorganic perovskite single crystals are being pursued intensively because of their reduced biological toxicity and enhanced material stability, greatly relieving two major bottlenecks of practical device applications. However, the investigation of their predicted photoelectric anisotropy is still absent, especially under visible and near‐infrared light illuminations. In this work, the high‐anisotropic photodetectors are reported based on Cs₃Bi₂I₉ single crystal sheets. The photoelectric performances are superior along the high‐conductance cleavage plane (001), exhibiting over two‐order magnitude anisotropy in contrast with that along the high‐resistance cross‐plane. Particularly, these anisotropies are varied with illumination wavelengths of different penetration depths. Moreover, the anisotropy is also evidently influenced by illuminate positions due to the lateral self‐driven effects. This work enriches anisotropic photoelectric exploration in lead‐free all‐inorganic perovskite materials and may motivate new strategies to achieve performance‐improved in‐plane photodetectors.