Low Effective Mass Leading to High Thermoelectric Performance

TL;DR

This paper demonstrates that low effective mass in thermoelectric materials like PbTe enhances power factor, challenging the traditional focus on high density of states and flat bands for thermoelectric performance.

Contribution

It provides a clear demonstration that low effective mass improves thermoelectric performance, emphasizing band structure engineering for low effective mass along the transport direction.

Findings

Low effective mass leads to higher power factor in PbTe.

Doping and temperature can tune the effective mass.

Deformation potential theory explains the impact of effective mass on thermoelectric performance.

Abstract

High Seebeck coefficient by creating large density of state (DOS) around the Fermi level through either electronic structure modification or manipulating nanostructures, is commonly considered as a route to advanced thermoelectrics. However, large density of state due to flat bands leads to large effective mass, which results in a simultaneous decrease of mobility. In fact, the net effect of high effective mass is a lower thermoelectric figure of merit when the carriers are predominantly scattered by acoustic phonons according to the deformation potential theory of Bardeen-Shockley. We demonstrate the beneficial effect of light effective mass leading to high power factor in n-type thermoelectric PbTe, where doping and temperature can be used to tune the effective mass. This clear demonstration of the deformation potential theory to thermoelectrics shows that the guiding principle for band structure engineering should be low effective mass along the transport direction.