Lead-free SnTe-based compounds as advanced thermoelectrics

Thermoelectric materials are able to realize the direct energy conversion between heat and electricity and have great potential in power generation and Peltier cooling. SnTe, an old but intriguing mid-temperature thermoelectric material, has attracted much attention in the past half-decade because of its non-toxic chemical elements as well as distinctive two-valence-bands (L and Σ bands) electronic structure. However, pristine SnTe shows inferior thermoelectric performance largely due to its intrinsically large population of holes as charge carriers, big energy difference between L and Σ bands and high lattice thermal conductivity. In recent years, numerous efforts have been carried out to optimize the transport coefficients of SnTe, endowing the peak thermoelectric figure of merit ZT above 1.8. In this review, the fundamental properties of SnTe are first outlined, and the optimization strategies are subsequently summarized for both electronic and phonon transport. Finally, future possible directions to further enhance the thermoelectric performance of SnTe are put forward at the end of this article. We believe that this review will spark people's inspiration in exploring other IV-VI thermoelectric compounds.