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, approximate to 20% reduction in the already ultralow lattice thermal conductivity is realized for the Sn0.99Na0.01Se-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 Sn0.99Na0.01Se-STSe sample.