The Electronic, Optical, Thermoelectric, and Structural Properties of a Cubic Double Perovskite X2agbibr6 (X=Li, Na, K, Rb, Cs): Ab-Initio Calculation

Structural, elastic, electronic, optical, and thermoelectric properties of cubic double perovskites X2AgBiBr6 (X=Li, Na, K, Rb, Cs) were calculated. Ab-initio calculations with various exchange-correlation potentials, e.g., LDA, GGA-PBE, GGA-WC, and hybrid functionals (HSE06), were carried out. The obtained results showed excellent agreement with the experimental and previous theoretical results. By calculating their structural and elastic properties, it was determined that X2AgBiBr6 compounds were ionically bonded, elastically stable, ductile, and anisotropic. Using HSE06, it was found that the compounds are semiconductors with indirect bandgaps at the (X- L) point, with bandgap values of 2.124, 2.222, 2.198, 2.209, and 1.902 eV for X2AgBiBr6 (X=Li, Na, K, Rb, and Cs), respectively. Due to their distinguishing optical characteristics and indirect wide bandgap, these compounds show promise as absorber layers for solar cells and other visible and ultraviolet-operating optoelectronic devices. Thermoelectric properties reveal that the number of free electrons and holes rises with temperature, the bandgap falls, and the specific heat increases. By investigating the Seebeck coefficient, electrical conductivity per relaxation time, Power factor, Figure of merit ZT, and thermal conductivity as a function of temperature for X2AgBiBr6 at Fermi energy, these compounds show that they can be employed in thermoelectric devices.