Tailoring Point Defects to Enhance Thermoelectric Performance in AgCuTe-Based Compounds.

Crystalline solids with intrinsically low lattice thermal conductivity are essential for advancing high-performance thermoelectric materials. Superionic conductor AgCuTe exhibits inherently low lattice thermal conductivity and exceptional tunability in both electronic and phononic transport, making it a promising candidate for medium-temperature thermoelectric applications. However, its practical deployment remains limited by suboptimal performance and insufficient optimization strategies. Here, we report a substantially enhanced dimensionless figure of merit (ZT) of ∼1.72 at 773 K in p-type polycrystalline AgCuTe through a systematic point defects engineering strategy. Guided by mass and strain field fluctuation criteria for suppressing lattice thermal conductivity, sulfur is identified as an effective dopant. Subsequent introduction of cation vacancies further synergizes electronic and thermal transport, yielding a high average ZT of 1.55 between 523-773 K, surpassing all previously reported values for AgCuTe. Moreover, a segmented single-leg thermoelectric module combining this material with commercial p-type (Bi, Sb)2Te3 achieves a high energy conversion efficiency of ∼13.7% under a temperature gradient of ∼467 K. These results underscore the efficacy of point defects engineering in optimizing superionic conductors and highlight the strong potential of AgCuTe for practical thermoelectric applications.