Ab initio prediction of the structural, electronic and optical behavior of novel combinations of ternary perovskite oxides ATiO3 (A = Rb, Cs, Fr) using the Hubbard ‘U’ correction for optoelectronic devices

The structural and optoelectronic properties of ATiO3 (A = Rb, Cs, and Fr) perovskite oxides in the cubic phase are investigated using an ab initio method based on density functional theory. The exchange correlation function is determined by the full-potential linearized augmented plane wave approach. RbTiO3 shows an indirect band gap energy of 2.43 eV, whereas direct band gap energies of 1.90 eV and 1.66 eV are calculated for CsTiO3 and FrTiO3 compounds, respectively. The electronic density of states reveals that d states from A-cations (Rb, Cs, and Fr), along with Ti-d states, are located in the conduction band. The charge density demonstrates the ionic nature of the A-cations (Rb, Cs and Fr), while oxygen atoms share isolines with Ti atoms, leading to covalent bonds between them. Optical analyses show that the considered compounds have good optical conductivity and absorptivity when high-energy photons are incident on the surface of the materials, in particular showing minimal reflectivity. In view of these results, we consider that perovskites belong to a semiconductor category of materials suitable for application in photovoltaic and optoelectronic devices.