Tunning of band gap of double perovskites halides Rb₂CuSbX₆ (X = Cl, Br, I) for solar cells and energy harvesting

The double perovskites (DPs) halides are outstanding materials for solar cells and thermoelectric applications. Therefore, here we have studied the electronic, optoelectronic, and thermoelectric properties of Rb₂CuSbX₆ (X = Cl, Br, I) by density functional theory. Thermodynamic and structural stabilities are validated by evaluating the enthalpy of formation and tolerance factor. The band gap calculations are calculated using TB-mBJ which indicate that the studied DPs have indirect band gaps. The band gap values are reduced from 1.0 eV to 0.46 eV with increasing size from Cl to I. This decreasing trend in bandgap values shift the absorption from visible to infrared region. The optical properties are analyzed by calculating dielectric constant, refractive index, reflectivity, and absorption coefficient. The performance of studied DPs is measured by power factor and figure of merit. Therefore, the analyses show the importance of these DPs for a wide spectrum of optoelectronic and thermoelectric applications to make devices for clean energy harvesting in future.