Study of electronic, mechanical, thermoelectric, and optical aspects of K2AlAg(Br/I)6 for solar cells, and energy storage applications

Double perovskite materials exhibit considerable potential in addressing global energy challenges and advancing renewable energy technologies. This study focuses on K2AlAg(Br/I)6 and employs a comprehensive DFT approach to explore its structural, mechanical, thermodynamic, optical, and thermoelectric properties. The structural and thermodynamic stabilities of K2AlAg(Br/I)6 are accurately examined through tolerance factor (τF) and formation energy analysis. The mechanical stability and ductile characteristics are affirmed by studying elastic constants, Passion's, and Pugh's ratios. Additionally, insights into hardness, Debye temperature, as well as transverse and longitudinal sound velocities contribute to a deeper understanding of the material's thermodynamic response. The band gap of K2AlAgBr6 is identified as 2.71 eV, which undergoes a reduction to 1.17 eV when Br is substituted with I, attributed to the pd-hybridization of cations and anions. Exploring optical properties reveals valuable information through dielectric constants ε(ω), refractive index (n(ω)), absorption (α(ω)), and reflectivity (R(ω)). Notably, absorption in both visible and ultraviolet ranges underscores the material's significance for solar cell applications. Furthermore, the computed ultralow lattice thermal conductivity and higher figure of merit are noteworthy outcomes, driven by the substantial Seebeck coefficient and electrical conductivity of the material. These results collectively highlight the exclusive and promising characteristics of K2AlAg(Br/I)6 in the area of renewable energy materials.