High Thermoelectric Performance in Polycrystalline SnSe Via Dual‐Doping with Ag/Na and Nanostructuring With Ag 8 SnSe 6

Abstract 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 Ag 8 SnSe 6 (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 (VBM 1 and VBM 5 ), 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 Ag 8 SnSe 6 , which further strengthens the scattering of phonons. Specifically, ≈20% reduction in the already ultralow lattice thermal conductivity is realized for the Sn 0.99 Na 0.01 Se–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 0.99 Na 0.01 Se–STSe sample.