Room‐Temperature Out‐of‐Plane Ferroelectricity and Resistance Switching Based on 2D Bi2O2Se

Abstract Although 2D Bi 2 O 2 Se plays an important role in the electronics and optoelectronics based on its in‐plane property, its out‐of‐plane electrical transport behavior remains unclear, especially in fabricating vertical devices with high integration density for novel functionality. Here, a solution‐processed method is developed to prepare 2D Bi 2 O 2 Se with mass production (e.g., hundreds of milliliter scale). The out‐of‐plane ferroelectric property of 2D Bi 2 O 2 Se is observed by piezoresponse force microscopy and the ferroelectric dipole map atom‐by‐atom at the Bi 2 O 2 Se surface, which shows an atomically resolved dipolar displacement of Se ions. The out‐of‐plane resistant switching property of 2D Bi 2 O 2 Se is revealed by conductive atomic force microscopy. Moreover, the electric field on the local polarization of Bi 2 O 2 Se is addressed by using ab initio simulations, which shows a broken inversion symmetry along the z‐axis of Bi 2 O 2 Se. The working mechanism of resistant switching behavior in Bi 2 O 2 Se is attributed to the diffusion and shuttle of Se ions. Besides, a controllable wet‐assembled method is developed to prepare Bi 2 O 2 Se thin film with centimeter scale and explores its application on photodetectors under 808 nm laser light. This work reveals the unique out‐of‐plane transport behavior of 2D Bi 2 O 2 Se, providing the basis for fabricating multifunctional devices with high integration based on this 2D material.