Structure Stability and Optical Response of Complex Lead Perovskite: A Computational Approach to Modeling of Perovskite Solar Cells

Abstract

This work presents a contribution to the study of the effect of bromide substitution on the structural, electronic, and optical properties of Rb₂AgSbCl₆ perovskite materials. To determine these different properties, we conducted simulations using the linearized augmented plane wave (FP-APW) method, which is based on density functional theory (DFT), employing the generalized gradient approximation (WC-GGA) to handle the exchange and correlation terms. The implementation of this method is carried out using the WIEN2K code. The calculated band gap energy for pure Rb₂AgSbCl₆ is approximately 2.08 eV, obtained using the modified Tran-Blaha (TB)–Becke Johnson (mBJ) exchange potential, which is in good agreement with experimental measurements. It was observed that the band gap values decrease as Br substitutes Cl at different concentrations of 25%, 50%, and 75%. Additionally, the band gap energy for Rb₂AgSbBr₆ was calculated, yielding a value of 1.34 eV. This study demonstrates that Br substitution enhances the hole and electron carrier mobility in pure Rb₂AgSbCl₆ compounds. Furthermore, optical analysis reveals that Br substitution improves the optical properties of Rb₂AgSbCl₆ by reducing transparency while enhancing the refractive index and absorption in the visible light region. By analyzing the Spectroscopically Limited Maximum Efficiency (SLME), the specific luminescent minority electron (SLME) of Rb₂AgSb(Cl₀.₅Br₀.₅)₆ was found to be 9.51%. Although this percentage is modest, it can be attributed to the indirect band gap nature of the material. Additionally, we calculated the thermoelectric properties, and the electronic properties indicate that these compounds are p-type semiconductors. Based on the obtained results, it is expected that the band gap, optical, and thermoelectric properties of Rb₂AgSbCl₆ perovskite can be effectively tuned by Br substitution at Cl sites, making Rb₂AgSb(Cl₁₋ₓBrₓ)₆ alloys promising candidates for optoelectronic and photovoltaic applications. Also we study the electronic properties of Rb₂AgSb₁₋ₓBiₓX'₆ alloys, where x takes values of zero, 0.25, 0.50, 0.75, and 1, with X′ representing Cl, Br, or I.