Sb Alloying for Engineering High-Thermoelectric zT of CuGaTe₂

Decades of studies on thermoelectric materials have enabled the design of high-performance materials based on basic materials properties, such as bandgap engineering. In general, bandgap energies correspond to the temperature at which the peak thermoelectric performance occurs. For instance, CuGaTe₂ with a relatively wide bandgap of 1.2 eV has its peak zT > 1 at > 900 K. On the other hand, the zT is usually very low (<0.1) for this material at room temperature. This severely limits its average zT and hence overall performance. In this study, a phase diagram-guided Sb alloying strategy to improve the low-temperature zT of CuGaTe₂ is used, by leveraging on the solubility limits to control the formation of the microstructural defects. The addition of Sb simultaneously improves the electrical conductivity and decreases the lattice thermal conductivity. For a low-temperature range of 300–623 K, this Sb-alloying strategy enables the achievement of a record high average zT of 0.33. The strategy developed in this study targets the improvement of the low-temperature range of CuGaTe₂, which is rarely focused on for wide-bandgap ABX₂ compounds, opening up more opportunities for holistic performance improvements, potentially enabling ultrahigh-performance thermoelectrics over a wide temperature range.