Realizing High Thermoelectric Performance in ZnCl-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 ZnCl 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 ZnCl doping, can significantly improve the electrical transport coefficient. Additionally, multiple defects caused by ZnCl 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-2%ZnCl sample achieves a maximum of ∼1.3 at 873 K parallel to the pressing direction, being 4 orders higher than that of the pristine SnSe 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.