A2AlInI6 (A = K, Rb, Cs) Double Perovskite Halides for Renewable Energy Applications: A DFT Study on Stability, Light Absorption, and Thermoelectric Performance

Abstract

Double perovskite halides are promising candidates for addressing energy scarcity and hold significant potential for renewable energy applications. In this study, the physical properties of A₂AlInI₆ (A = K, Rb, or Cs) compounds were investigated using density functional theory (DFT) and the all-electron FP-LAPW method. The optimized structural parameters and negative formation energies confirm that these halides are structurally and thermodynamically stable in their cubic phase. Mechanical analysis reveals that K₂AlInI₆ exhibits a ductile nature, as indicated by its Pugh and Poisson ratios, while Rb₂AlInI₆ and Cs₂AlInI₆ demonstrate brittle characteristics. Electronic band structure calculations yield energy bandgaps of 2.10 eV, 2.08 eV, and 1.98 eV for K₂AlInI₆, Rb₂AlInI₆, and Cs₂AlInI₆, respectively, suggesting strong potential for light absorption in the visible spectrum. Optical properties, including the complex dielectric function, indicate superior absorption in the UV and visible ranges, further supporting their application in solar energy systems. Solar cell efficiency, evaluated using the Spectroscopic Limited Maximum Efficiency (SLME) approach via Jarvis software, confirms their suitability for photovoltaic devices. Additionally, thermoelectric properties were analyzed using semi-classical Boltzmann theory. At room temperature, the figure of merit (ZT) values for the compounds were found to be 0.74, 0.72, and 0.71, respectively. These values highlight their potential for integration into hybrid renewable energy systems, combining photovoltaic and thermoelectric functionalities.