Lead-Free Double Perovskites Rb2TlSbX6 (X=Cl, Br, and I) As an Emerging Aspirant for Solar Cells and Green Energy Applications

This study utilized the WIEN2k simulation program to examine the structural, mechanical, thermodynamic, optoelectronic, and thermoelectric characteristics of lead-free double perovskites Rb2TlSbX6 (X=Cl, Br, and I). The objective is to assess their potential contribution to next-generation photovoltaic and thermoelectric systems. The ab initio molecular dynamics (AIMD) has validated that materials are thermodynamically stable. Examining mechanical features confirms the mechanical stability and ductile characteristics of studied perovskites. Rb2TlSbCl6 exhibits superior flexibility and stiffness, whereas Rb2TlSbI6 demonstrates the highest level of anisotropy. The thermodynamic parameters confirm the thermal stability and stronger bonding at elevated pressure and temperature. The electronic features, determined by implementing the GGA-PBE and TB-mBJ functionals, indicate direct band gaps at the Gamma- Gamma position. The band gap ranges from 1.22 eV to 1.74 eV, 0.94 to 1.34 eV, and 0.81 eV to 1.15 eV for Rb2TlSbCl6, Rb2TlSbBr6, and Rb2TlSbI6, respectively. The analyzed optical characteristics reveal significant absorption and conductivity with decreased reflectance and optical loss between 0 and 6 eV. Rb2TlSbI6 has the greatest dielectric constant, which suggests a lower recombination rate of electronhole pairs. The thermoelectric characteristics demonstrate a large figure of merit values of 0.78, 0.80, and 0.84 at room temperature. Therefore, these materials have the significant capability for solar cell technology and may effectively convert thermal energy into usable electrical power.