Multiscale-defects Simultaneous Optimization of Thermoelectric Performance in the n-Type Polycrystalline SnSe via (Zr, Cl) Co-doping

SnSe crystals have attracted considerable attention in thermoelectric due to their outstanding performance. However, the mechanical properties of crystals are poor and the synthesis of crystals is usually associated with complex processes. Polycrystalline SnSe materials are more advantageous for practical applications. Herein, a strategy of constructing multiple lattice defects by (Zr, Cl) co-doping is proposed, which is effective in realizing simultaneously optimized electrical and thermal transport properties. The multiscale-defects play the key roles in regulating thermoelectric properties: the foreign ions have entered into the lattice of matrix, causing the tuned carrier concentration, and the produced conductive precipitates along the grain boundaries benefit for maintaining the carrier mobility. In addition, multiscale lattice defects, such as pores, dislocations and precipitates, are favor of enhancing the phonon scattering for lowering lattice thermal conductivity. The STEM analysis and lattice thermal conductivity model calculations confirm the effects of various mechanisms on reducing the thermal conductivity in the (Zr, Cl) co-doped polycrystalline SnSe materials. Ultimately, a high ZT value of 1.42 is obtained at 773 K for the optimum specimen, and the average ZT within the temperature range of 573−773 K reaches 1.01. These results suggest that the strategy of (Zr, Cl) co-doping can simultaneously improve the thermoelectric performance in n-type SnSe materials, which might be worth promoting in other systems.