In this paper, we study the structural, electronic and optical properties of the inorganic solar perovskites XPbBr3 (X= Li or Na). We applied the two methods: the density functional theory (DFT) and time-dependent density-functional theory (TDDFT). In fact, we performed the DFT method using the Quantum Espresso package. Also, the total energies of the studied inorganic solar perovskites XPbBr3 (X= Li or Na) have been deduced as a function of the lattice parameter a (Å). The two calculation methods have been carried out under the GGA-PBE and GGA-PBESol approximations. Moreover, the total and partial density of states (DOS) and the band structure of the studied compounds have been presented and discussed for the two cases: with and without the spin orbit coupling (SOC) approximation. In addition, the DFT and TDDFT have been explored in order to elaborate the structural, the electronic and the optical properties of the inorganic perovskite CsPbI3 material for solar cell applications. When using the GGA-PBESol method without SOC approximation, we found a band gap energy value greater than that one computed when adding the SOC correction. On the other hand, the optical properties of the studied material have been studied. In particular, we found that the inorganic solar Perovskite XPbBr3 (X=Li or Na) materials exhibit a high transparency of the electromagnetic radiations in energy range between 0 eV and 33 eV.

In this paper, we use the density functional theory (DFT) calculations under Quantum Espresso package to characterize the doping effect of sulfur substituting on the Zirconium dioxide ZrO2. Through the density of states and the band structure calculations, a direct band gap is appearing for the pure and doped studied system. The electronic properties analysis shows that the doping with sulfur could considerably decrease the band gap of doped ZrO2 by the presence of an impurity state of sulfur 3 p on the up spin of the valence band. The results of the ab-initio density functional theory investigations show that the substitutional sulfur dopants incorporated into the Zirconium dioxide ZrO2 drastically and affect the electronic structure of the studied material. In fact, the doping of Zirconium dioxide ZrO2 with appropriate concentration values of sulfur leads to band gap values in the interval (1-2) eV. We recall that the band structure and density of states can improve among others: the energy gap of this doped ZrO2 material. In fact, we have started from 1.3 eV for the pure ZrO2 to reach 1.2 eV for 9% of sulfur doping. This last energy gap value is suitable for photovoltaic application.