Band Convergence in Thermoelectric Materials: Theoretical Background and Consideration on Bi-Sb-Te Alloys

Band engineering is one of core approaches to improve the performance of thermoelectric materials via the Seebeck coefficient enhancement. However, the conclusion that is often found in the literature is that the band engineering has been achieved in haste when a simple increase in a density-of-states effective mass is observed. In this review, a theoretical background to the band convergence, the most effective band engineering strategy to improve the thermoelectric power factor, is provided. In addition, a straightforward reasoning that can be employed to distinguish the occurrence of band convergence in the observed Seebeck coefficient increase is presented with Bi-Sb-Te-based alloys as an example. We expect that this review will be served as a practical guide for the composition-controlled material design to improve the electronic transport properties in thermoelectric materials on the basis of the band engineering route.