Exploring the structural, Mechanical, electronic, optical, and thermoelectric properties of Cesium-based double perovskite Cs2GeSnX6 (X = Cl, Br, I) compounds: A DFT study

The Cubic Cs2GeSnX6(X = Cl, Br, I) double perovskite's structural, thermoelectric, electronic , and optical properties are examined within the framework of density functional theory (DFT). The outcomes of the formation energy (Delta H) and tolerance factor (tau f) validate the cubic phase stability of the Cs2GeSnX6(X = Cl, Br, I) compounds. Direct bandgap (Eg) values for Cs2GeSnCl6, Cs2GeSnBr6, and Cs2GeSnI6 are 1.79 eV, 1.04 eV, and 0.47 eV, correspondingly. Simulations are also conducted for optical properties including refractive index, optical conductivity, reflection, absorption, and dielectric constants (epsilon 1, epsilon 2). High reflectivity and a high absorption coefficient demonstrate that these materials are perfect for optoelectronic applications, such as solar and photovoltaic cells. Additionally, the BoltzTraP2 Code is employed to evaluate the thermoelectric properties. These compounds are promising for thermoelectric applications since their calculated figures of merit (zT) for Cs2GeSnCl6, Cs2GeSnBr6, and Cs2GeSnI6 are 0.97, 0.96, and 0.89, respectively.