Effect of Pb-Sn substitution on the structural, electronic, optical, and thermodynamic properties of CsPb₁₋ₓSnₓBr₃ (x = 0.25 and 0.75): A DFT study

Halide perovskites have emerged as promising materials for optoelectronic and photovoltaic applications owing to their outstanding optoelectronic properties and tunable band gaps. Among them, all-inorganic halide perovskites have attracted significant attention because their structural, electronic, and optical properties can be effectively tailored through B-site cation substitution. However, the composition-dependent behavior of intermediate Pb/Sn ratios in cubic CsPb1-xSnxBr3 remains insufficiently explored, particularly through accurate atomic modeling of substituted configurations. In this work, the effect of partial Pb/Sn substitution on the
structural, electronic, optical and thermodynamic properties of cubic CsPb1-xSnxBr3 with Sn concentrations of x = 0.25 and x = 0.75 was systematically investigated using first-principles calculations. Ordered 2 × 2 × 1
supercell models were employed to represent the Pb/Sn distribution, while density functional theory (DFT) calculations were performed using the Wu–Cohen generalized gradient approximation (WC-GGA) for structural
optimization. The electronic and optical properties were further evaluated using the KTB-mBJ exchange potential. The calculated band gaps are 1.45 eV for x = 0.25 and 1.67 eV for x = 0.75, accompanied by static
dielectric constants of 3.12 and 3.85, respectively. The increase in Sn concentration leads to a slight widening of the band gap and induces noticeable modifications in the optical response. Furthermore, the thermodynamic
properties were analyzed within the quasi-harmonic Debye model, revealing a physically consistent temperaturedependent behavior characterized by gradual lattice softening while maintaining structural stability over the
investigated temperature range. The calculated E–V curves confirm the favorable structural stability of both investigated compositions within the considered configurations. These results demonstrate that controlled Pb/Sn
substitution provides an effective approach for tailoring the electronic, optical and thermal characteristics of CsPb1-xSnxBr3.This study provides new insights into the composition-dependent properties of intermediate Pb–Sn
bromide perovskites and contributes to the rational design of optimized inorganic perovskite materials for optoelectronic applications.