Synthesis, Bottom up Assembly and Thermoelectric Properties of Sb-Doped PbS Nanocrystal Building Blocks

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.

Colloidal synthesis of the mixed ionic-electronic conducting NaSbS2 nanocrystals

Solution-based synthesis of mixed ionic and electronic conductors (MIECs) has enabled the development of novel inorganic materials with implications for a wide range of energy storage applications. However, many technologically relevant MIECs contain toxic elements (Pb) or are prepared by using traditional high-temperature solid-state synthesis. Here, we provide a simple, low-temperature and size-tunable (50-90 nm) colloidal hot injection approach for the synthesis of NaSbS2 based MIECs using widely available and non-toxic precursors. Key synthetic parameters (cationic precursor, reaction temperature, and ligand) are examined to regulate the shape and size of the NaSbS2 nanocrystals (NCs). FTIR studies revealed that ligands with carboxylate functionality are coordinated to the surface of the synthesized NaSbS2 NCs. The synthesized NaSbS2 nanocrystals have electronic and ionic conductivities of 3.31 × 10-10 (e-) and 1.9 × 10-5 (Na+) S cm-1 respectively, which are competitive with the ionic and electrical conductivities of perovskite materials generated by solid-state reactions. This research gives a mechanistic understanding and post-synthetic evaluation of parameters influencing the formation of sodium antimony chalcogenides materials.

Synergistic effect of grain boundaries and phonon engineering in Sb substituted Bi2Se3 nanostructures for thermoelectric applications

Phonon scattering by intrinsic defects and nanostructures has been the primary strategy for minimizing the thermal conductivity in thermoelectric materials. In this work, we present the effect of Isovalent substitution as a method to decouple the Seebeck coefficient and the thermal conductivity of antimony (Sb) substituted bismuth selenide (Bi₂Se₃). Transmission electron microscopy studies present the nanostructured Bi_2-xSb_xSe₃ thermoelectric system represents the coexistence of hierarchical defect structure and dislocations. The observed giant reduction in thermal conductivity is due to the multi-scale phonon scattering caused by a combination of stacking faults, lattice dislocations and grain boundary scattering. This study reveals that a large number of dislocations about ∼1.09 × 10¹⁶ m^-2 are particularly effective at lowering thermal conductivity. We achieved one of the ultra-low thermal conductivity values (∼0.26 W/m K) for the maximized dislocation concentration. Moreover, Isovalent substitution provides a new avenue for the reduction in thermal conductivity and significant enhancement in the Seebeck coefficient of thermoelectric materials.