Extending the temperature range of the Cmcm phase of SnSe for high thermoelectric performance

Thermoelectric power generation requires high dimensionless figure of merit ZT across broad temperatures. The two-dimensional phonon and three-dimensional charge transports enable n-type-Pnma tin selenide (SnSe) crystals to show a peak ZT of ~3.0 at 748 kelvin. In this work, we focused on the high-symmetry Cmcm phase to boost two-dimensional phonon and three-dimensional charge transports and extended the high-performance (ZT ~ 3.0) plateau. By simultaneously broadening the Cmcm-phase stability window and enhancing lattice symmetry through lead alloying, we extended the high performance from a single temperature point to a wide temperature range of ~250 kelvin in rock salt-like Cmcm SnSe crystals rendered n-type through chlorine doping. An average ZT of ~3.0 was achieved between 673 and 923 kelvin, with a conversion efficiency of ~19.1% under a temperature difference of ~572 kelvin.