Synthesis of n-type SnSe polycrystals with high and isotropic thermoelectric performance

Abstract

p-type SnSe has the ultrahigh thermoelectric ZT over 2 at 773 K, as single crystal with a significantly anisotropic structure or polycrystals. In this study, a facile route of synthesizing n-type polycrystalline SnSe, which has high and isotropic thermoelectric performance, is proposed using simple ball milling, pre-annealing and spark plasma sintering processes, in sequence. The pre-annealing process effectively changes the major carrier from hole to electron and increases the crystallinity and grain size of the SnSe powder. The addition of SnCl2 as a dopant enables the electron concentration to be controlled in the range of 1.3 × 1016 cm−3 to 1.7 × 1018 cm−3 at 300 K. As a result, a remarkable ZT of 0.84–0.86 at 773 K was achieved for n-type polycrystalline SnSe0.92 with 4 wt% SnCl2, regardless of the sintering direction.