Cation Modulation in AgSbTe2 Realizes Carrier Optimization, Defect Engineering, and a 7% Single‐Leg Thermoelectric Efficiency

Abstract AgSbTe 2 plays a pivotal role in mid‐temperature thermoelectric generators (TEGs). Leveraging the seminal advances in cation manipulation within AgSbTe 2 , this study demonstrates an enhanced TE power factor ( PF = S 2 σ ) of 1.5 mWm −1 K −2 and a peak zT of 1.5 at 583 K in an off‐stoichiometric Ag 1.04 Sb 0.96 Te 2 crystal. The introduction of Ge in place of Ag leads to an increased n H as evidenced by the detection of trace Ge 4+ through XPS analysis. Further chemical state analysis reveals the simultaneous presence of Ag + , Sb 3+ , and Ge 4+ , elucidating the effect of cation modulations. TEM characterizations validate the presence of superlattice structure, and the linear defects discerned within the AgSbTe 2 matrix. Consequently, the lattice thermal conductivity κ L is substantially reduced in the Ag 1.02 Ge 0.02 Sb 0.96 Te 2 crystal, yielding a peak zT of 1.77 at 623 K. This notable advancement is attributed to the counterbalance achieved between the enhanced PF and the reduced κ L , facilitated by cation modulation. Additionally, a single‐leg TE device incorporating Ag 1.02 Ge 0.02 Sb 0.96 Te 2 demonstrates a conversion efficiency of 7% across a temperature gradient (ΔT) of 350 K. This study corroborates the efficacy of cation modulation through thermodynamic approaches and establishes a relationship between transport properties and the presence of defects.