Realizing high thermoelectric performance in SnSe<sub>2 </sub><i>via</i> intercalating Cu

Abstract

SnSe, a layered material with intrinsic low thermal conductivity, is reported to have excellent thermoelectric properties. SnSe<sub>2</sub> has a similar structure to SnSe, but the SnSe<sub>2</sub> has a low electrical transport, resulting in a poor thermoelectric performance, and the intrinsic SnSe<sub>2</sub> has a maximum <i>ZT</i> value of only ~ 0.09 at 773 K. In this work, SnSe<sub>1.98</sub>Br<sub>0.02</sub>-<i>y</i>%Cu (<i>y</i> = 0, 0.50, 0.75, 1.0) bulk materials are synthesized by the melting method combined with spark plasma sintering (SPS) based on the carrier concentration improved through Br doping. In the SnSe<sub>2</sub> materials with van der Waals chemical bonding between layers, the synergistic effects of intercalating Cu on the thermoelectric properties are investigated. On the one hand, the extra Cu not only provides additional electrons but also can be embedded stably in the van der Waals gap and form an intercalated structure, which is beneficial to the charge transfer in or out of the layers, and thus synergistically improving the carrier concentration and carrier mobility. On the other hand, owing to the dynamic Cu doping, the increase of carrier concentration compensates for the decrease of carrier mobility caused by carrier-carrier scattering, which maintains the high electrical transport properties at high temperature. The present results show that at room temperature, the power factors along the parallel and perpendicular to the SPS (//<i>P</i> and ⊥<i>P</i>) sintering directions increase from ~0.65 and ~0.98 µW·cm<sup>–1</sup>·K<sup>–2</sup> for intrinsic SnSe<sub>2</sub> to ~10 and ~19 μW·cm<sup>–1</sup>·K<sup>–2</sup> for SnSe<sub>1.98</sub>Br<sub>0.02</sub>-0.75%Cu samples, respectively. Finally, at 773 K, the maximum <i>ZT</i> value of ~0.8 is achieved along the ⊥<i>P</i> direction. This study proves that the SnSe<sub>2</sub> greatly promises to become an excellent thermoelectric material.