First-principles study of the surface energies and electronic structures of γ-CsSnI₃ surfaces

All-inorganic perovskite CsSnI₃ has attracted intense research interests due to its prominent optoelectronic properties, high thermal stability, and environmentally friendly character. The surface energies and electronic structures of black orthorhombic (γ) CsSnI₃ surfaces are investigated by using first-principles methods. The anisotropic and termination-dependent surface energies of low-index surfaces (i.e., the (110), (001), (100) and (101) surfaces) are obtained, providing important data for CsSnI₃, since these values are difficult to be measured in experiments. The CsI-terminated (110) and (001) surfaces are predicted to be the most stable and their surface energies are close, making the cube-shape of nanocrystals favorable at thermodynamic equilibrium, which is consistent with the experimental observations. Calculated surface electronic structures show that the quantum confinement effect is orientation dependent. The band gaps of the (100) and (101) surfaces are significantly larger than those of the (110) and (001) surfaces by using slabs with similar thickness. This distinction can be attributed to different 'electronic dimensionalities' of these surfaces. Our results provide physical insights into the thermodynamic stability and electronic properties of CsSnI₃ surfaces.