Modulated Fermi Level and Relaxed Lattice Strain Leading to Enhanced Thermoelectric Properties in AgSbSe₂

Abstract

Cubic-phase AgSbSe2 has been known as a decent p-type thermoelectric material, due to its intrinsically low lattice thermal conductivity; nevertheless, the difficulty in modulating its electrical transport performance impeded its further competition with other state-of-the-art mid-temperature thermoelectrics. In this work, we investigated the effects of Pb doping and Sb vacancies on modulating the thermoelectric properties of AgSbSe2. Pb doping was found to be able to obviously increase the hole concentration, leading to a descending of Fermi level well into the multiple valence bands, thus leading to an enhanced band degeneracy; subsequent Sb vacancies could play the role of relaxing the local lattice strains due to PbSb substitution, resulting in a weakened charge carrier scattering and enhanced weighted mobility. Consequently, a peak power factor PF max of 7.5 μW cm–1 K–2 at 523 K was achieved in the composition of AgSb0.935Pb0.06Se2, which is 40% higher than that of pristine AgSbSe2. Furthermore, Pb doping and Sb vacancies induce enhanced point defect scattering of high-frequency heat-carrying phonons, yielding a reduced lattice thermal conductivity and a remarkably enhanced maximal ZT max value of 1.02 at 723 K in the sample AgSb0.935Pb0.06Se2.

Surface Chemistry and Band Engineering in AgSbSe2: Toward High Thermoelectric Performance

“…(a) Temperature-dependent zT values of AgSbSe 2 , AgSb 0.98 Sn 0.02 Se 2 –OL, and surface-treated AgSb 0.98 Sn 0.02 Se 2 (LD stands for ligand displacement). (b) Comparison of the temperature-dependent zT values obtained for AgSb 0.98 Sn 0.02 Se 2 in the present work with previously reported state-of-the-art AgSbSe 2 -based TE materials. − , …”

“…Aliovalent doping is commonly employed to tune the carrier concentration of AgSbSe 2 . Specifically, the substitution of the trivalent Sb 3+ ions by divalent Pb 2+ , − Cd 2+ , Zn 2+ , Ca 2+ , Mg 2+ , Ba 2+ , and Mn 2+ , and monovalent Na + , or even Ag + through generating Ag-rich and Sb-deficient Ag 1+x Sb 1– x Se 2 , has been employed to reach hole densities up to 10 19 cm –3 thereby improving σ to achieve zT values above unity (Figure b). Recently, we have also reported a solution-based strategy to produce Bi 3+ -doped AgSbSe 2 reaching zT values up to 1.1 at 640 K through the synergistic effects of carrier engineering, nanostructuring, and bond anharmonicity …”