First-principles study of opto-electronic and thermoelectric properties of SrCdSnX4 (X=S, Se, Te) alkali metal chalcogenides

In the present research, chalcogenide materials SrCdSnX 4 (X = S, Se, Te) were investigated in terms of electronic, optical, and thermoelectric properties by first-principles calculations based on density functional theory (DFT). The exchange-correlations potential was settled from generalized gradient approximation (GGA) in Perdew, Burke and Ernzerhof (PBE) and modified Becke Johnson (mBJ) approximations within the framework of full-potential linearized augmented plane wave method (FPLAPW). The band structure calculations show the semiconducting nature of materials containing direct bandgaps 3.25 eV, 3.08 eV, and 1.90 eV for SrCdSnX 4 (X = S, Se, Te), respectively. The electronic and optical profile of investigated materials exhibits a strong hybridization due to S/Sn/Se/Te-p and Cd/Sr-d orbitals. It is observed that SrCdSnTe 4 material shows better absorption in the visible range while the other two materials are good in the ultraviolet region. The optical dispersion analysis of complex dielectric function ε (ω), energy loss function L(ω), refractive index n(ω), extinction coefficient k(ω), reflectivity R(ω), and optical conductivity σ(ω) were also analyzed in the energy range of 0–14 eV. The computed optical results of all investigated materials show an anisotropy polarization of all compounds, making them suitable in optoelectronic device application. The transport properties of chalcogenide compounds were also computed by Post-DFT (Boltztrap) simulation code. The electrical conductivity (σ/τ), electronic thermal conductivity (κe/τ), and Seebeck coefficient (S) of SrCdSnX 4 (X = S, Se, Te) observed semiconducting nature due to majority carriers of electrons. The effective masses of electrons and holes were also computed by fitting dispersion curves. These results show that the nature of bands changed from the inflection point at 0.6, from direct to indirect for chalcogenides SrCdSnX 4 (X = S, Se, Te).