Ab-inito simulation of the structural, electronic and optical properties for the vacancy-ordered double perovskites A2TiI6 (A = Cs or NH4); a time-dependent density functional theory study

Abstract

In the present work, we have performed a detail analysis of the established Ti-based perovskites compounds and calculated the structural, electronic and optical properties of the vacancy-ordered double perovskites A2TiI6 (A = Cs+ or NH4+) that simulated using ab-initio approach within the framework of density functional theory (DFT) and time-dependent DFT (TDDFT). The Ti-based halide perovskites possess several interesting properties, including high stability, suitable band gap and excellent optical absorption. The calculations predict a direct band gap that is in agreement with the reported values. The real and imaginary parts of the dielectric function ε(ω), absorption coefficient α(ω), reflective index R(ω), refractive index n(ω), extinction coefficient k(ω), energy loss spectrum L(ω) and the real part of optical conductivity have been calculated. The obtained results show good agreement with the available experimental results, particularly in the low-energy region of the spectra. Based on a suitable direct band gap and strong absorption coefficient, these materials are suitable candidates for photovoltaic applications and are suggested as ideal potential materials for single-junction solar cells.