First-principles calculations to investigate structural, optoelectronics and thermoelectric properties of lead free Cs2GeSnX6 (X = Cl, Br)

In the present investigation, we examined the structural, elastic, electronic, optical as well as thermoelectric features of Cs2GeSnX6 (X = Cl, Br) double perovskite compounds employing FP-LAPW method depended on density functional theory applied to WIEN2k. The tolerance factor, formation energy, and phonon dispersion all provide predictions about the structural stability of Cs2GeSnX6 (X = Cl, Br). The electronic feature of the Cs2GeSnX6 (X = Cl, Br) is determined employing GGA and mBJ. Using mBJ, the band gap is computed to be 1.37 eV, 0.91 eV, for Cs2GeSnX6 (X = Cl, Br) respectively. Insight into the mechanical stability of the material is provided by the computed elastic constants. The compounds under investigation are found to be ductile by nature as evidenced from computed elastic constants. It was determined that the compounds might be used in optoelectronic and photovoltaic devices from evaluated refractive index, reflectivity etc. The transport properties are computed in terms of Seebeck coefficient, power factor, electrical conductivity within 200 to 900 K tem-perature range. Cs2GeSnX6 (X = Cl, Br) has relatively high PFs of around 4.50 x 1011 W/K2ms and 5.35 x 1011 W/K2ms, respectively, reflecting their potential usage in thermoelectric devices. The viability of the Cs2GeSnX6 (X = Cl, Br) for use in thermoelectric and photovoltaic applications by having extensive absorption patterns and excellent PF.