Transition metal–based quaternary chalcogenides have attracted immense attention for various renewable energy applications, including thermoelectric (TE) devices. While low symmetry and a complex structure help to achieve low thermal conductivity, the TE power-factor and hence the figure of merit ($ZT$) remain low, which hinders use of this class of materials for future TE applications. Here we investigate the TE properties of a system, ${\mathrm{Cu}}_2{\mathrm{Zn}\mathrm{Si}\mathrm{Te}}_4$, with improved electronic transport using first-principles calculations. The presence of a heavy chalcogen such as $\mathrm{Te}$ helps to achieve a relatively low band gap (0.58 eV). This, together with unique electronic band topology, leads to promising values of the power-factor of 5.8 mW ${\mathrm{m}}^{-1}$ ${\mathrm{K}}^{-2}$ ($n$-type conduction) and 3.8 mW ${\mathrm{m}}^{-1}$ ${\mathrm{K}}^{-2}$ ($p$-type conduction) at 900 K. $\mathrm{Te}$ atoms also play a crucial role in mixing the optical and acoustic phonon branches, which, in turn, are responsible for reduced lattice thermal conductivity (approximately $0.86$ W ${\mathrm{m}}^{-1}$ ${\mathrm{K}}^{-1}$ at high temperature). Although the thermal conductivity is not appreciably low, the electronic transport properties (power-factor) are quite favorable and yield a promising TE figure of merit ($ZT\sim 2.40$ for $n$-type conduction and $ZT\sim 1.94$ for $p$-type conduction at 900 K). We propose ${\mathrm{Cu}}_2{\mathrm{Zn}\mathrm{Si}\mathrm{Te}}_4$ as a potential candidate for TE applications, and believe it will attract experimental and theoretical studies.

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• Electrical conductivity
• Electron relaxation
• Lattice thermal conductivity
• Seebeck effect
• Thermoelectrics
• Ab initio calculations