Chemical trends of electronic properties of two-dimensional halide perovskites and their potential applications for electronics and optoelectronics

Two-dimensional (2D) halide perovskites with the formula of A₂M^IVX₄^VII are now emerging as a new family of 2D materials and promising candidates for nanoelectronics and optoelectronics. Potentially, there could be abundance of 2D halide perovskites by varying the compositions of A, M and X and their properties can be widely tuned to satisfy the requirements of the practical applications. While several samples have been experimentally realized, most of them are currently unexplored and their chemical trends in relation to the chemical compositions are yet not well understood, which thus drags down the exploration of their potential applications. In this work, using first-principles calculation methods, we systematically investigate the properties of 2D halide perovskites, including their structural stabilities, electronic, optical, and transport properties. The chemical trends in this novel family of 2D materials are established and we find that the bandgaps increase with increased lattice distortions by changing A ion from Cs⁺ to CH₃NH₃⁺, increase with M^IV ion changing from Sb to Pb, and decrease with X changing from Cl to Br to I. Some of the studied systems like Cs₂SnI₄ are identified with good optical properties for photovoltaics and most of the systems have good motilities suitable for electric devices like transistors. The abundance of potential 2D halide perovskites not only enriches current 2D families but also offers more possibility for electrical and optoelectrical applications. Our work is expected to provide theoretical understanding and guidance for the further study of these 2D halide perovskites.