High Thermoelectric Performance of Co-Doped P-Type Polycrystalline SnSe via Optimizing Electrical Transport Properties

This work systematically investigated the thermoelectric properties of p-type Na and M (M = K, Li, Ag) codoped polycrystalline SnSe. It is found that the electrical properties of polycrystalline SnSe can be improved significantly for (Na, Ag) codoped samples, contributed by the enhanced carrier concentration. Specifically, a carrier concentration of 6.23 × 10¹⁹ cm^-3 was obtained in Sn_0.98Na_0.016Ag_0.004Se sample at 335 K, an increase of 18% compared with that of the Na single-doped sample (5.22 × 10¹⁹ cm^-3). The power factor reached ∼0.73 mW m^-1 K^-2 for the Sn_0.98Na_0.016Ag_0.004Se sample at 785 K, enhanced by ∼26% compared with Na single-doped one. In addition, Sn-rich and Ag-rich particles/areas observed in the matrix of Sn_0.98Na_0.016Ag_0.004Se contribute to the reduction of lattice thermal conductivity from 0.61 W m^-1 K^-1 for Sn_0.98Ag_0.02Se to 0.47 W m^-1 K^-1 at 785 K. The combination of simultaneously enhanced power factor and depressed thermal conductivity leads to a maximum ZT ≈ 1.2 at 785 K and a high average ZT ≈ 0.74 at 335-785 K for Sn_0.98Na_0.016Ag_0.004Se, and generating a high theoretical conversion efficiency of ∼11%. These illuminating discoveries could provide routes to enhance the thermoelectric performance in p-type polycrystalline SnSe.