High Thermoelectric Performance in Polycrystalline SnSe Via Dual-Doping with Ag/Na and Nanostructuring With Ag₈SnSe₆

Single crystalline SnSe is one of the most intriguing new thermoelectric materials but the thermoelectric performance of polycrystalline SnSe seems to lag significantly compared to that of a single crystal. Here an effective strategy for enhancing the thermoelectric performance of p-type polycrystalline SnSe by Ag/Na dual-doping and Ag₈SnSe₆ (STSe) nanoprecipitates is reported. The Ag/Na dual-doping leads to a two orders of magnitude increase in carrier concentration and a convergence of valence bands (VBM₁ and VBM₅), which in turn results in sharp enhancement of electrical conductivities and high Seebeck coefficients in the Ag/Na dual-doped samples. Additionally, the SnSe matrix becomes nanostructured with dispersed nanoprecipitates of the compound Ag₈SnSe₆, which further strengthens the scattering of phonons. Specifically, ≈20% reduction in the already ultralow lattice thermal conductivity is realized for the Sn_0.99Na_0.01Se–STSe sample at 773 K compared to the thermal conductivity of pure SnSe. Consequently, a peak thermoelectric figure of merit ZT of 1.33 at 773 K with a high average ZT (ZT_ave) value of 0.91 (423–823 K) is achieved for the Sn_0.99Na_0.01Se–STSe sample.