Science http://doi.org/bbmx (2015)

Thermoelectric materials generate power when a temperature gradient is applied across them, and hence are of substantial interest for the recovery of waste heat. As such, high performance thermoelectrics — characterized by a large thermoelectric figure of merit, ZT — typically exhibit large electrical conductivity, but low thermal conductivity. Although a number of high-ZT materials have been reported, a pressing need exists to develop systems that exhibit this performance over a wide temperature range, not just at a single temperature. Writing in Science, Zhao et al. hole-doped layered SnSe single crystals, achieving a ZT of 0.7–2.0 in the temperature range of 300–773 K along the crystallographic b axis. Although the ultralow thermal conductivity of SnSe along the b axis had been reported previously, hole doping leads to a remarkable enhancement in both electrical conductivity and the Seebeck coefficient, rationalizing the impressive performance. High ZT over the reported temperature range results in an expected maximum conversion efficiency of almost 17%.