Thermoelectric power factor: Enhancement mechanisms and strategies for higher performance thermoelectric materials

Thermoelectric research has witnessed groundbreaking progress over the past 15-20 years. The thermoelectric figure of merit, ZT, a measure of the competition between electronic transport (i.e. power factor) and thermal transport (i.e. total thermal conductivity), has long surpassed once a longtime barrier of ∼1 and thermoelectric scientists are targeting ZT > 2 as the new goal. A majority of this recent improvement in ZT has been achieved through the reduction of lattice part of thermal conductivity (κl) using nanostructuring techniques. The rapid progress in this direction focused the efforts on the development of experimental methods and understanding phonon transport to decrease lattice thermal conductivity. This fact left the development of ideas to improve electronic transport and thermoelectric power factor rather overlooked. With thermal conductivity of the potential thermoelectrics approaching the minimum theoretical limit, on the journey to higher ZT values, a paradigm shift is necessary toward the enhancement of the thermoelectric power factor. This article discusses the ideas and strategies proposed and developed in order to improve the thermoelectric power factor and thus hopefully move us closer to the target of a ZT > 2!