Density FunctionalTheory Study of Surface Stabilityand Phase Diagram of Orthorhombic CsPbI₃

CsPbI₃ has been recognized as a promising candidate for optoelectronic device applications. To further enhance device efficiency, it is imperative to understand the surface properties of CsPbI₃, which affect the charge transport and defect formation. In this study, we conducted density functional theory calculations to explore the stability of the (001), (110), and (100) surfaces of orthorhombic CsPbI₃, considering different stoichiometries and surface reconstructions. Our results show that under the chemical potentials confined by the thermodynamically stable region of bulk CsPbI₃, the CsI-terminated surfaces of (001) and (110) and the stoichiometric surface of (100) are stable. Among these three surfaces, the CsI-terminated (110) surface has the lowest surface energy and no midgap states, which benefits the transport properties of the material.