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

Abstract

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 SnSe1-x materials would affect the repeatability of thermoelectric performance. Herein, the thermoelectric properties of n-type polycrystalline SnSe0.95-based composites are highly enhanced by heterogeneous Cu doping. The carrier concentration of the SnSe0.95 material was optimized by SnCl2 doping. The strategy of heterogeneous Cu doping is employed in further improving the thermoelectric performance of the SnCl2-doped SnSe0.95 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 SnSe0.95-1 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.