High Thermoelectric Performance in n-Type PbSe via Embedding Coherent Endotaxial Nanostructure

PbSe has been regarded as a potential candidate for replacing state-of-the-art thermoelectric (TE) PbTe-based materials, owing to the scarcity of Te. In contrast to the progress in a p-type counterpart, effective strategies to enhance TE performance of n-type PbSe have been rare until recently. For example, band convergence to decouple Seebeck coefficients and electrical conductivity for higher power factor has not been possible because of a large energy gap between first and second conduction bands in contrast to the case of its p-type version. As a result, TE performance of n-type PbSe has been improved by reducing thermal conductivity.<br/>In this presentation, we report a new high-performance n-type PbSe thermoelectric system embedded with a very low concentration nanoscale, semiconducting alloys. Through atomic-resolved TEM, we observed the formation of coherent interfaces between the surrounding matrix and endotaxial nanostructures. The coherent nanostructure gives additional phonon scattering mechanisms induced by mass fluctuation across the interface, remarkably suppressing a lattice thermal conductivity down to ~0.32 W m^–1 K^–1. Concurrently, incorporating alloys effectively manipulate the electronic band structure, consequently increasing the conduction band effective mass maximum and a magnitude of Seebeck coefficient. Both effects synergistically improve the TE performance, showing a record-high TE figure of merit, ZT, of ~2.0 at 823 K, for all n-type PbSe and PbTe-based materials to date. This result shows that the strategy of designing coherent endotaxial nanostructures could be an effective means of controlling charge and thermal transport properties independently.