DFT aided prediction of phase stability, optoelectronic and thermoelectric properties of A2AuScX6 (A= Cs, Rb; X= Cl, Br, I) double perovskites for energy harvesting technology

Abstract: In this work, density functional theory (DFT) is used to find out the ground state structures of A2AuScX6 (A= Cs, Rb; X= Cl, Br, I) double Perovskite (DP) halides for the first time. The DP A2AuScX6 halides were studied for their structural phase stability and optoelectronic properties in order to identify potential materials for energy harvesting systems. The stability criteria were verified by computing the formation energy, binding energy, phonon dispersion curve, stiffness constants, tolerance, and octahedral factors. The electronic band structure, carrier effective mass, density of states (DOS), and charge density distribution were calculated to reveal the nature of electronic conductivity and the chemical bonding nature present within them. For Cs2AuScX6 (Rb2AuScX6) [X = Cl, Br, I], the corresponding values of band gap [using TB-mBJ] are 1.88 (1.93), 1.68 (1.71), and 1.30 (1.32) eV. The optical constants (dielectric function, absorption coefficient, refractive index, energy loss function, photoconductivity, and reflectivity) were also calculated to get more insights into their electronic nature. For Cs2AuScX6 (Rb2AuScX6) [X = Cl, Br, I], the absorption coefficient in the visible range are 3.33 (3.45) 105 cm-1, 2.70 (2.81) 105 cm-1, and 2.13 (2.18) 105 cm-1, respectively. We also investigated the thermoelectric properties to predict promising applications in thermoelectric devices. Our calculations revealed high ZT values of 0.92, 1.07, and 1.06 for Cs2AuScX6 (X = Cl, Br, I) and 0.97, 0.99, and 1.01 for Rb2AuScX6 (X = Cl, Br, I) at 300 K. To further aid in predicting any novel materials, routine research was also done on the thermo-mechanical characteristics. The results suggest the compounds considered as potential candidates for use in solar cells and/or thermoelectric devices.