Investigation of Structural, Electronic and Optical Properties of Na2InAgCl6, K2InAgCl6, and Rb2InAgCl6 Lead-Free Halide Double Perovskites Regarding with Cs2InAgCl6 Perovskites Cell and a Comparative Study by DFT Functionals

Electronics band structures, the total density of state, the partial density of state and optical properties were investigated by DFT method for A2InAgCl6 (A= Cs, Na, K, and Rb). Moreover, the band gap of Na2InAgCl6, K2InAgCl6, Rb2InAgCl6 and Cs2InAgCl6 were calculated at 1.039 eV, 1.041 eV, 1.039 eV and 1.089 eV by GGA with PBE, 0.784 eV, 0.769 eV, 0.775 eV and 0.770 eV by LDA with CA-PZ and 1.310 eV, 1.152 eV, 1.180 eV and 1.169 eV by GGA with RPBE functionals. The density of states (DOS) and partial density of states (PDOS) were evaluated. Among of used functionals, GGA with RPBE functional has considered the appropriate and acceptable method for calculation of band gap where the 1.310 eV of band gap was reported for Cs2InAgCl6, which is close to experimental value at 1.370 eV. The crystal, Na2InAgCl6, has considered as the best perovskites cell among other four due to low band gap, and the main cause is revealed that it has attached the lightest Na atom to convey the low band gap as lower surface or atomic size atom.