Tuning the properties of ASnTe (A = Li, Na, K, Rb, Cs) chalcogenide perovskites for optimal solar energy conversion: computational insights.

This study explores the structural, electronic, optical, mechanical, and thermodynamic properties of ASnTe (A = Li, Na, K, Rb, and Cs) chalcogenide perovskites using density functional theory (DFT). The stability of these materials was assessed by calculating formation energies, Goldschmidt tolerance factors ( ), Bartel tolerance factor (), and phonon dispersion. Electronic structure calculations show indirect band gaps ranging from 0.27 to 1.32 eV, with minimal direct-indirect offsets (0.06-0.23 eV), indicating strong potential for both photovoltaic (Rb, Na, CsSnTe) and thermoelectric (Li, KSnTe) applications. Carrier type analysis reveals p-type behavior for Na, K, Rb, and Cs analogues, and n-type for LiSnTe. Mechanical properties were comprehensively assessed using elastic constants, moduli, Poisson's ratio, Pugh's ratio, machinability index, Vickers hardness, and universal and Zener anisotropy indices, supported by 2D and 3D elastic modulus visualizations. All compounds exhibit elastic anisotropy and good ductility, with NaSnTe identified as the most ductile (Poisson's ratio > 0.30, / > 1.75). Vickers hardness varies from 0.99 GPa (KSnTe) to 1.77 GPa (RbSnTe), and KSnTe demonstrates superior machinability (3.05), favoring its practical processability. Thermodynamic parameters-including entropy, enthalpy, free energy, and heat capacity, were derived from phonon dispersion calculations. The materials also exhibit low lattice thermal conductivity (0.27-0.38 W m K), high melting points (771-892 K), and favorable Debye temperatures (126-158 K). These results highlight ASnTe perovskites as promising, lead-free candidates for multifunctional applications, including solar energy conversion, thermoelectrics, thermal barrier coatings, and flexible electronics.