Influence of surface engineering on the transport properties of lead sulfide nanomaterials.

Lead Sulfide (PbS) has garnered attention as a promising thermoelectric (TE) material due to its natural abundance and cost-effectiveness. However, its practical application is hindered by inherently high lattice thermal conductivity and low electrical conductivity. In this study, we address these challenges by surface functionalization of PbS nanocrystals using Cu₂S molecular complexes-based ligand displacement. The molecular complexes facilitate the incorporation of Cu into the PbS matrix and leads to the formation of nanoscale defects, dislocations, and strain fields while optimizing the charge carrier transport. The structural modulations enhance the phonon scattering and lead to a significant reduction in lattice thermal conductivity of 0.60 W m^-1K^-1 at 867 K in the PbS-Cu₂S system. Simultaneously, the Cu incorporation improves electrical conductivity by increasing both carrier concentration and mobility with carefully optimized the content of Cu₂S molecular complexes. These synergistic modifications yield a peak figure-of-merit (zT) of 1.05 at 867 K for the PbS-1.0 %Cu₂S sample, representing an almost twofold enhancement in TE performance compared to pristine PbS. This work highlights the effectiveness of surface treatment in overcoming the intrinsic limitations of PbS-based materials and presents a promising strategy for the development of high-efficiency TE systems.