Stable lead free double perovskites Cs₂XAu(Br/I)₆ (X = Y, Sc) as an emerging aspirant for solar cells and thermoelectric applications

In present article, the electronic, optical, mechanical, and thermoelectric characteristics of Cs₂XAu(Br/I)₆, where X = Y, Sc are addressed comprehensively. The Born stability criteria ensure the mechanical stability, whereas the structural, thermodynamic, and lattice stabilities are calculated from tolerance factor, formation energy, and phonons dispersion band structures. The ductility, hardness, lattice thermal conductivity, melting, and Debye temperatures are discussed in terms of elastic constants. The direct band gaps 1.90/1.35 eV Cs₂ScAu(Br/I)₆, and 2.23/1.74 eV for Cs₂YAu(Br/I)₆ fall the absorption of light energy in visible to near ultraviolet regions. The Cs₂ScAuI₆ has ideal band gap (1.35 eV) for solar cells because broad absorption band in visible region. Finally, thermoelectric behavior has been studied by Seebeck coefficient, electrical conductivity, power factor, and thermal conductivity in the temperature range 200 K–600 K. The highest figure of merit (1.0 at 300 K) for Cs₂YAuBr₆ increases demand for thermoelectric generators.