Colloidal nanocrystal assembly enables composition and doping engineering for high-performance PbS-based thermoelectrics

Lead sulfide (PbS) is a promising thermoelectric material due to its low cost, excellent thermal stability, and abundance of constituent elements. As a narrow-bandgap semiconductor, PbS possesses high carrier mobility and intrinsically low lattice thermal conductivity, providing a favorable platform for performance optimization. While recent advances in doping, nanostructuring, and defect engineering have significantly improved its figure of merit (ZT), further enhancement requires simultaneous tuning of both electrical and thermal transport. In this work, we developed a bottom-up colloidal nanocrystal assembly strategy to precisely control the composition and microstructure of PbS-based materials. Partial substitution of sulfur with selenium markedly reduced the room-temperature thermal conductivity from 1.18 to 0.58 W m−1 K−1 (≈50% reduction) while improving the power factor, yielding a maximum ZT of 1.12 for the PbS0.4Se0.6 composition. Building on this, aliovalent Gd doping was introduced into PbS0.4Se0.6 to synergistically increase carrier concentration and mobility. Although Gd incorporation slightly raised the thermal conductivity, the significant boost in power factor led to an overall improvement in thermoelectric performance, achieving a peak ZT of 1.33 at 879 K.