Studies on Thermoelectric Properties of n-type Polycrystalline SnSe_1-xS_x by Iodine Doping

Iodine-doped n-type SnSe polycrystalline by melting and hot pressing is prepared. The prepared material is anisotropic with a peak ZT of ≈0.8 at about 773 K measured along the hot pressing direction. This is the first report on thermoelectric properties of n-type Sn chalcogenide alloys. With increasing content of iodine, the carrier concentration changed from 2.3 × 10¹⁷ cm^-3 (p-type) to 5.0 × 10¹⁵ cm^-3 (n-type) then to 2.0 × 10¹⁷ cm^-3 (n-type). The decent ZT is mainly attributed to the intrinsically low thermal conductivity due to the high anharmonicity of the chemical bonds like those in p-type SnSe. By alloying with 10 at% SnS, even lower thermal conductivity and an enhanced Seebeck coefficient were achieved, leading to an increased ZT of ≈1.0 at about 773 K measured also along the hot pressing direction. For the first time, TE properties of n-type Sn chalcogenide polycrystal materials are reported. By doping with iodine, the n_H changes from 2.3 × 10¹⁷ cm^-3 (p-type) to 5.0 × 10¹⁵ cm^-3 (n-type) then to 2.0 × 10¹⁷ cm^-3 (n-type). By alloying with SnS, the lowered thermal conductivity and enhanced Seebeck coefficient contribute to a highest ZT of ≈1.0 at 773 K for SnSe_0.87S_0.1I_0.03 polycrystals.