Band structure and absorption spectra of NH4XI3 (X = Pb, Mg) based hybrid Perovskite for UV ray protector and electrochromic materials applications

Abstract

Modeling Perovskite materials and tuning their properties by monovalent or divalent cations substitution produce several choice Perovskite compounds, studied extensively to improve the power conversion efficiency, reduce toxicity, and enhance stability. We modeled NH4PbI3 and NH4MgI3 from the parent compound CH3NH3PbI3, by replacing the monovalent CH3NH3+ with NH4+ and the divalent Pb atom with Mg. In this study, the electronic band structure, as well as the electronic bandgaps, were calculated using the Perdew-Burke-Enzenhoff (PBE) and Perdew-Burke-Enzenhoff for solid (PBEsol) exchange-correlation functionals of the Density-functional Theory (DFT) and GW quasiparticle method of the Many-Body Perturbation Theory (MBPT). Similarly, we used Time-Dependent Density Functional Perturbation Theory (TDDFPT) and the solution of the Bethe-Salpeter equation (BSE) of the Many-Body Perturbation Theory to determine the real and imaginary dielectric tensors with and without spin-orbit coupling (SOC). Direct bandgaps at R high symmetry point were reported for NH4PbI3, while NH4MgI3 showed indirect bandgaps at Γ→R high symmetry points with lower bandgaps compared to NH4PbI3. The projected density of state around the Fermi level reveals that the iodine (I) p orbital is most responsible for the valence band in both NH4PbI3 and NH4MgI3, while the Lead (Pb) p orbital and the Magnesium (Mg) s orbitals, show the most prominent contribution to the Conduction bands. Similar Optical spectra were achieved with BSE-SOC, TDDFPT, and TDDFPT-SOC for NH4PbI3 without the absorption onsets, while NH4PbI3 predicts higher values of absorbance and absorption coefficient compared to NH4MgI3 which predict lower reflectivity and higher transmittance. Both compounds show maximum absorption coefficient in the order of 105 in the ultraviolet region like CH3NH3PbI3 and silicon. Therefore, we suggest that NH4PbI3 will be useful as solar cell absorber and UV ray protector, while NH4MgI3 would have more applications in the production of electrochromic materials.