Strategies to advance earth-abundant PbS thermoelectric

The earth-abundant PbS is a sister compound of PbTe and PbSe, and attracts increasing research interests from thermoelectric community. Owning to its strong Pb-S chemical bonding, PbS compound presents higher mechanical properties than that in PbTe and PbSe analogues, such as hardness and Young's modulus, which are favorable to thermoelectric device fabrication. However, the strong chemical bonding in PbS lattice will reversely cause relatively low carrier transport properties and high thermal conductivity compared with other lead chalcogenides, thus restricting its thermoelectric performance. Such distinct features give PbS compound different approaches to optimize its thermoelectric performance. In this perspective, we discuss these effective strategies to advance PbS-based thermoelectric materials by introducing some important progresses recently developed from following aspects: carrier density optimization, band structure manipulations to tune carrier effective mass, band alignment to maintain high carrier mobility and defect design to block phonon transport. Both n-type and p-type PbS systems are included and separately discussed due to their different optimizing strategies. Finally, some possible strategies are proposed to further improve thermoelectric performance in PbSbased materials.