Heterogeneous Cu Doping Facilitates Excellent Thermoelectric and Mechanical Performance in n-Type SnSe Composites

SnSe materials have attracted extensive attention in thermoelectrics due to their low thermal conductivity. Nevertheless, the thermoelectric properties of n-type polycrystalline SnSe are still low, and metallic Sn distributed in the SnSe_1–x materials would affect the repeatability of thermoelectric performance. Herein, the thermoelectric properties of n-type polycrystalline SnSe_0.95-based composites are highly enhanced by heterogeneous Cu doping. The carrier concentration of the SnSe_0.95 material was optimized by SnCl₂ doping. The strategy of heterogeneous Cu doping is employed in further improving the thermoelectric performance of the SnCl₂-doped SnSe_0.95 materials. In addition, partial Cu⁺ doping tunes the electron concentration to enhance the Seebeck coefficient. Moreover, metallic Sn distributed along the grain boundaries can be stabilized by forming Cu₆Sn₅ alloys, which improve the thermal stability of bulk composites. Excessive Cu particles and SnCl₂ precipitates strengthen phonon scattering for lowering the lattice thermal conductivity. Ultimately, a peak ZT of 1.55 is yielded at 773 K in the SnSe_0.95–1 wt % SnCl₂–1 wt % Cu bulk composite, whose mechanical hardness is also increased. Hence, these results promote a feasible approach to simultaneously enhance the thermoelectric and mechanical properties of n-type SnSe-based composites, which might be worth exploring in other thermoelectric materials.