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 SnSe0.95–2%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 SnSe0.95 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.