Non‐Centrosymmetric 2D Nb₃SeI₇ with High In‐Plane Anisotropy and Optical Nonlinearity

Abstract Integrating anisotropy and nonlinearity of physical properties in 2D materials is of great importance to the progress of nanoelectronic, nanophotonic, and nano‐optoelectronic applications. In this work, Nb 3 SeI 7 , a newly discovered ternary layered material with non‐centrosymmetric lattices, is introduced, which exhibits strong second harmonic generation (SHG), in‐plane anisotropic electricity, and light absorption. Symmetry breaking of 2D Nb 3 SeI 7 induced by the polar off‐center displacement of niobium leads to a high nonlinear optical response with a second‐order susceptibility of 6.71 pm V −1 and a high anisotropic factor of photoresponsivity up to 4.6, which are higher than most of the 2D materials. These properties of 2D Nb 3 SeI 7 create new possibilities for chip‐integrated nonlinear optics devices and future‐proof polarization‐sensitive optoelectronic systems.