Realizing High Thermoelectric Performance in ZnCl2-Doped N-Type Polycrystalline SnSe Through Band Engineering and Incorporating Multiple Defects

SnSe-based compounds, as promising thermoelectric materials, are well-known for their intrinsically low thermal conductivity and outstanding thermoelectric performance. However, the suboptimal electrical transport capacity for n-type polycrystalline SnSe significantly hinders the improvement of its thermoelectric performance. In this work, an effective approach for enhancing the thermoelectric performance of n-type SnSe polycrystalline materials through ZnCl₂ doping has been investigated. The enhanced density of state effective mass, which is related to the introduction of an impurity level and the facilitation of multivalley degeneracy after ZnCl₂ doping, can significantly improve the electrical transport coefficient. Additionally, multiple defects caused by ZnCl₂ doping, such as multiscale precipitates, amorphous tin chloride, and twin boundaries, effectively decrease the lattice thermal conductivity, leading to a subsequently enhanced quality factor. As a result, the SnSe_0.95-2%ZnCl₂ sample achieves a maximum zT of ∼1.3 at 873 K parallel to the pressing direction, being 4 orders higher than that of the pristine SnSe_0.95 sample and better than that of most other halide-doped SnSe samples. This study presents a cost-effective and environmentally friendly strategy for improving the thermoelectric properties of n-type polycrystalline SnSe.