First principle study of lead-free double perovskites halides Rb₂Pd(Cl/Br)₆ for solar cells and renewable energy devices: A quantum DFT

Lead-free double perovskites are promising materials for environmental friendly photovoltaics and other optoelectronics. In this article, optical, thermoelectric, and thermodynamic properties of Rb₂Pd(Cl/Br)₆ are explored by modified Becke and Johnson potential. The Goldschmidt tolerance factor (0.90-1.04) ensures the cubic phase is structurally stable. The negative formation energy and positive phonon dispersion authenticate the thermodynamic stability. The band gap of Rb₂PdCl₆ is 1.88 eV, which reduces to 1.21 eV by replacing Cl with Br anion. The first absorption regions (620-413)nm for Rb₂PdCl₆ and (826-496)nm for Rb₂PdBr₆ increase their solar cells' implication. The transport properties are investigated by Boltzmann transport theory through the BoltzTraP code. Finally, the high values 0.76 and 0.75 of the figure of merit at room temperature also ensure their importance for thermoelectric generators.