Electronic structures and properties of lead-free cesium- or rubidium-based perovskite halide compounds by first-principles calculations

•Electronic structures of Rb- and Cs-based Pb-free perovskites were investigated.•Sn-based perovskites had higher carrier mobilities compared with other perovskites.•Halogen substitutions affected the total energies and energy gaps.•Total energies were closely related with the tolerance factors.