Computational insights into structural, electronic, optical and thermoelectric features of ternary chalcogenide Ca2GeX4 (X=S, Se, Te) compounds

Abstract

The advancements in materials engineering for clean energy and greenhouse gas reduction has attracted global attention. Furthermore, the distinct electrical and optical properties of ternary chalcogenides are critical for their application in solar energy conversion. In this study, the electronic, optical, thermodynamic, and thermoelectric transport properties of the ternary chalcogenide Ca₂GeX₄ (X = S, Se, and Te) compounds are comprehensively investigated using the density functional theory-based WIEN2k package. The findings indicate that ternary chalcogenide Ca₂GeX₄ compounds possess substantial band gaps and display strong covalent bonding characteristics. Analysis of the density of states reveals minimal impact from S-s and S-p states, while highlighting the significance of Ca-s and Ge-s states. The investigated materials show significant UV absorption with reflectance between 30 and 40 % which peaks at 13.5 eV at about 65 %, confirming the optical properties of the ternary chalcogenide Ca₂GeX₄. The positive Seebeck coefficient suggests that holes are the primary charge carriers in tested materials, with thermal energy rising in accordance with the chalcogenide's atomic number. Several thermoelectric properties that demonstrate the suitability of these materials for thermoelectric applications were also discussed. Overall, the findings confirm the thermoelectric and optoelectronic properties of Ca₂GeX₄ materials, which may facilitate the creation and development of effective optoelectronic devices.