Stability, mechanical, optoelectronic and thermoelectric behaviors of inorganic metal halide double perovskites (Cs2, K2, Rb2)SnCl6: Promising green energy alternatives

Density functional theory calculations were performed on the stability, mechanical, optoelectronic and thermoelectric characteristics for halide double perovskites (Cs2, K2, Rb2)SnCl6. This study focuses on the effects of temperature and chemical potential on electrons transport in these materials. Key transport results include maximum Seebeck coefficient of 1500 mu VK-1 at 300 K, maximum power factor of 2.5 1011 Ws-1K-2 at 300 K and maximum electrical conductivity (sigma/tau)x1019 Wm- 1K- 1s- 1 of 11, 6 and 9 at 300 K for (Rb2, Cs2, K2)SnCl6. High Seebeck coefficient and high electrical conductivity prove the existence of covalent bonding between Cl-3p site and (Cs-6p, K-4S, Rb-5s) states with weak van der Waals type interactions, which is also confirmed by adsorption analysis. The charge transfer is taking place via Cl-3p and (Cs-6p, K-4S, Rb-5s) states between upper valence band and lower conduction band. The estimated power factor offers useful guidelines for tuning and improving the thermoelectric performance. The density of states predicts the n-type conductivity in all compounds which was confirmed from positive value of Seebeck coefficient.