Study of lead-free double perovskites halides Cs2TiCl6, and Cs2TiBr6 for optoelectronics, and thermoelectric applications

Abstract

The vacancy ordered double perovskites are attractive materials for applications in optoelectronics, and other renewable energy technologies. In this research work, we have addressed the electronic, optical, thermoelectric, and thermodynamic properties of Cs2TiCl6 and Cs2TiBr6 double perovskites. The structural and dynamical stability is ensured by Goldsmith tolerance factor and positive phonon frequencies, respectively. The elastic constants, Poisson's, and Pugh's ratio show the mechanical stability and ductile behavior. Their ultralow thermal conductivity appears as important factors for device fabrication. The band structures reveal indirect band gaps 2.87eV, and 2.17eV for Cs2TiCl6 and Cs2TiBr6, respectively. The optical analysis has been done using the computed dielectric constant, absorption coefficient and refractive index. Thermoelectric calculations are executed using BoltzTraP code to investigate the electrical conductivity, thermal conductivity and Seebeck coefficient. The computed figure of merit (0.75 for Cs2TiCl6 and 0.78 for Cs2TiBr6) at room temperature reveals their excellent potential renewable energy applications.