High thermoelectric performance and low thermal conductivity in K-doped SnSe polycrystalline compounds

SnSe single crystal showed a high thermoelectric zT of 2.6 at 923 K mainly due to an extremely low thermal conductivity 0.23 W m(-1) K-1. It has anisotropic crystal structure resulting in deterioration of thermoelectric performance in polycrystalline SnSe, providing a low zT of 0.6 and 0.8 for Ag and Na-doped SnSe, respectively. Here, we presented the thermoelectric properties on the K-doped KxSn1-xSe (x = 0, 0.1, 0.3, 0.5, 1.5, and 2.0%) polycrystals, synthesized by a high-temperature melting and hot-press sintering with annealing process. The K-doping in SnSe efficiently enhances the hole carrier concentration without significant degradation of carrier mobility. We find that there exist widespread Se-rich precipitates, inducing strong phonon scattering and thus resulting in a very low thermal conductivity. Due to low thermal conductivity and moderate power factor, the K0.001Sn0.999Se sample shows an exceptionally high zT of 1.11 at 823 K which is significantly enhanced value in polycrystalline compounds.