Structural, electronic, mechanical, optical and thermoelectric properties of double perovskites A2CuAlCl6 (A=Cs, Rb, K) with direct bandgap using DFT study

Abstract

In this study, density functional theory (DFT) calculations were employed to investigate the structural, electronic, optical and elastic properties of the lead-free double perovskite compounds A₂CuAlCl₆ (A = Cs, Rb, K). These materials present a promising alternative for solar cell applications due to their reduced toxicity compared to lead-based perovskites. The structural stability was ensured by calculating the formation energy of these materials. Further to check the dynamic stability we calculated the phonon dispersion curve. The electronic properties were studied by examining the band structure and density of states. The electronic properties indicate the semiconducting nature of these materials. The band gap is found to be 1.70 eV, 1.76 eV and 1.86 eV are observed for Cs₂CuAlCl₆, Rb₂CuAlCl₆ and K₂CuAlCl₆ respectively. Additionally, we calculated the elastic constants to explore the mechanical properties of these materials and we found that all these materials are mechanically stable and have ductile nature. To understand the optical behavior, various parameters such as like refractive index, complex dielectric function, optical conductivity and absorption coefficient were studied. Besides, the temperature dependent thermoelectric properties are studied and figure of merit are found to be 0.62, 0.65 and 0.78, for K₂CuAlCl₆, Rb₂CuAlCl₆, and Cs₂CuAlCl₆ respectively at 700 Κ. The results suggest that these materials are highly suitable candidates for solar cell and thermoelectric applications due to their favorable properties.