Modifying electronic bandgap by halide ions substitution to investigate double perovskites Rb2AgInX6 (X = Cl, Br, I) for solar cells applications and thermoelectric characteristics

The demand for renewable and clean energy increases the significance of perovskites and attracts the substantial interest of the scientific community to further explore these materials owing to their excellent optoelectronic characteristics. In this regards, a DFT-approach was employed to investigate double perovskite's "Rb2AgInX6 (X = Cl, Br, I)" structural, electronic, optical and thermoelectric properties. To prove the structural and thermo-dynamic stability, the tolerance factor (tF) and formation energy (Delta Hf) were computed whose values falls within acceptable stable region. Based on the band structure (BS) calculations, the compounds demonstrate direct band gaps of the values of 2.16 eV, 1.32 eV, and 0.46 eV for anions Cl, Br, and I based-double perovskites, respectively. The band gap of 1.32 eV of Rb2AgInBr6 is ideal for exploring this compound for solar cell applications. Furthermore, to study optical characteristics, the investigated compounds were explored in terms of optical absorption, refractive index, and dielectric constants for energy range 0-6 eV which ensured the absorption among infrared, visible, and ultraviolet regions. Based on maximum absorption for visible region, the studied compound Rb2AgInCl6 is an excellent candidate to harvest solar cell applications, among others. Furthermore, the Seebeck coefficient, lattice thermal and electric conductivities, and figure of merit (ZT) addressed by Boltzmann theory also make them decent aspirants for thermoelectric applications.