Heterogeneous Cu\nDoping Facilitates Excellent Thermoelectric\nand Mechanical Performance in n‑Type SnSe Composites

SnSe materials have attracted extensive attention in\nthermoelectrics\ndue to their low thermal conductivity. Nevertheless, the thermoelectric\nproperties of n-type polycrystalline SnSe are still low, and metallic\nSn distributed in the SnSe<sub>1–<i>x</i></sub> materials\nwould affect the repeatability of thermoelectric performance. Herein,\nthe thermoelectric properties of n-type polycrystalline SnSe<sub>0.95</sub>-based composites are highly enhanced by heterogeneous Cu doping.\nThe carrier concentration of the SnSe<sub>0.95</sub> material was\noptimized by SnCl<sub>2</sub> doping. The strategy of heterogeneous\nCu doping is employed in further improving the thermoelectric performance\nof the SnCl<sub>2</sub>-doped SnSe<sub>0.95</sub> materials. In addition,\npartial Cu<sup>+</sup> doping tunes the electron concentration to\nenhance the Seebeck coefficient. Moreover, metallic Sn distributed\nalong the grain boundaries can be stabilized by forming Cu<sub>6</sub>Sn<sub>5</sub> alloys, which improve the thermal stability of bulk\ncomposites. Excessive Cu particles and SnCl<sub>2</sub> precipitates\nstrengthen phonon scattering for lowering the lattice thermal conductivity.\nUltimately, a peak ZT of 1.55 is yielded at 773 K in the SnSe<sub>0.95</sub>–1 wt % SnCl<sub>2</sub>–1 wt % Cu bulk composite,\nwhose mechanical hardness is also increased. Hence, these results\npromote a feasible approach to simultaneously enhance the thermoelectric\nand mechanical properties of n-type SnSe-based composites, which might\nbe worth exploring in other thermoelectric materials.