A comprehensive DFT Study of the electronic structure and optical properties of Iodine-based halide double perovskites for photovoltaic applications

This study aims to explore the electronic structure, thermodynamic, mechanical stability, and optical response of Iodine-based ordered vacancy double halide perovskite compounds through the application of density functional theory. The two compounds Cs₂ZrI₆ and Rb₂ZrI₆ exhibit thermodynamic stability, with displaying particularly notable. Moreover, analysis of the calculated coefficients of elastic stiffness confirms the mechanical stability of all materials under ambient pressure conditions. By using the Density Functional Theory with Spin-Orbit Coupling (SOC), it was observed that Cs2TeI6 and Rb2TeI6 possess an indirect band gap located between the X and L high-symmetry points, this show that Cs₂TeI₆, Rb₂ZrI₆, Cs₂HfI₆, and Rb₂HfI₆ are identified as direct semiconductor compounds. Moreover, the band gap values of X₂YI₆ (where X = Cs, Rb, and Y = Te, Zr, and Hf) exhibit an increasing trend as we progress along the alkali and transition metal elements in the periodic table, ranging from 1.422 eV for Cs₂TeI₆ to 2.465 eV for Rb₂TeI₆. Besides, the optical behavior of the visible light show that X₂YI₆ compounds have a high absorption of about 70%, reflectance of 30%, and a low transmittance. Thanks to their advantageous bandgap, enduring stabilities, and effective absorption of visible light, Cs₂TeI₆ and Rb₂TeI₆ hold significant promise for a wide range of electronic and optoelectronic applications, particularly in photovoltaics.