Limit of zT enhancement in rocksalt structured chalcogenides by band convergence

Rocksalt structured chalcogenides, such as PbTe, PbSe, and SnTe, are the top candidates for midtemperature thermoelectric applications, and their p-type thermoelectric efficiencies can be enhanced via aligning the valence bands. Here, we provided comprehensive numerical investigations on the effects of band convergence on electronic properties. We found that the extra valance band can indeed significantly enhance the power factor. Nevertheless, the extra valance band can also increase the electronic thermal conductivity, which partially offsets the enhanced power factor for the overall figure of merit. Finally, we predicted that the maximum figure of merit for PbTe, PbSe, and SnTe can reach 2.2, 1.8, and 1.6, respectively, without relying on the reduction in lattice thermal conductivity.