Defect-Engineering-Stabilized AgSbTe₂ with High Thermoelectric Performance

Thermoelectric (TE) generators enable the direct and reversible conversion between heat and electricity, providing applications in both refrigeration and power generation. In the last decade, several TE materials with relatively high figures of merit (zT) have been reported in the low- and high-temperature regimes. However, there is an urgent demand for high-performance TE materials working in the mid-temperature range (400–700 K). Herein, p-type AgSbTe₂ materials stabilized with S and Se co-doping are demonstrated to exhibit an outstanding maximum figure of merit (zT_max) of 2.3 at 673 K and an average figure of merit (zT_ave) of 1.59 over the wide temperature range of 300–673 K. This exceptional performance arises from an enhanced carrier density resulting from a higher concentration of silver vacancies, a vastly improved Seebeck coefficient enabled by the flattening of the valence band maximum and the inhibited formation of n-type Ag₂Te, and ahighly improved stability beyond 673 K. The optimized material is used to fabricate a single-leg device with efficiencies up to 13.3% and a unicouple TE device reaching energy conversion efficiencies up to 12.3% at a temperature difference of 370 K. These results highlight an effective strategy to engineer high-performance TE material in the mid-temperature range.