Exploring the Optoelectronic Attributes, Thermoelectric and Photocatalytic Potential of Double Perovskites Cs2BB'H6 (B = Al, Na and B'=Tl, In): A DFT Study

Double perovskites Cs2BB'H6 (B = Al, Na and B'=Tl, In) have been scrutinized by employing density functional theory to calculate their electronic structures, thermodynamic stability, elastic, optical, thermoelectric and photocatalytic properties. The FP-LAPW is utilized in the WIEN2k code for the calculations. Exchange correlation potentials such as modified Becke-Johnson with the addition of spin -orbital coupling are employed. The positive phonon frequencies, negative formation energies and optimization curves of the structures endorse the complete stability of studied perovskites. Mechanical properties also provide evidence of the structure's stability. Both compounds exhibit a semiconductor nature with an indirect bandgap of 2.38 eV and 2.51 eV for Cs2AlTlH6 and 3.34 eV and 3.40 eV for Cs2NaInH6 with mBJ and mBJ+SOC potentials, respectively. The partial and total densities of states have been computed to investigate the orbital's contribution. Calculations for optical response show the lowest energy loss and highest absorption in the ultraviolet range validating their use in optoelectronic devices. In addition, the evaluated thermoelectric response reveals their strong potential to use in renewable energy applications. Photocatalytic properties show the excellent response of both compounds for solar hydrogen synthesis.