Enhancement of Thermoelectric Performance of Layered SnSe₂ by Synergistic Modulation of Carrier Concentration and Suppression of Lattice Thermal Conductivity

Eco-friendly and low-cost layered SnSe2-based materials have been attracting great attention in the thermoelectric field for their intrinsically low thermal conductivity. In this work, we applied AgCl as Cl-dopant and formed Ag-rich precipitates in SnSe2 polycrystals, and their thermoelectric properties were investigated. The results demonstrate that Cl was artificially incorporated into SnSe2 by the substitution of Se atoms, playing as donor centers and thus increasing the carrier concentration by 2 orders of magnitude, leading to a tremendous improvement of the electrical conductivity and power factor. However, Ag atoms hardly enter into the Sn lattice sites and brought about the generation of Ag-rich precipitates. The complicated microstructures with multiple types of defects, such as point defects, boundaries, dislocations, and so on, result in a relatively low lattice thermal conductivity in the AgCl-introduced SnSe2 samples. Additionally, the anisotropic electrical and thermal transport properties were investigated, and the results show that higher ZT values were obtained along the pressing direction in these textured samples because of the significantly suppressed lattice thermal conductivity caused by the enhanced phonon scattering via the interior van der Waals layers. Ultimately, a maximum ZT value of 0.35 was realized at 400 °C in the polycrystalline SnSe2 with introduction of 11 mol % AgCl, which is nearly 3 times higher than that value of the pristine counterpart. It demonstrates that the combined effects of Cl-doping, Ag-rich precipitates, and texturing could effectively enhance the ZT value for polycrystalline SnSe2.