Large-Scale Colloidal Synthesis of Chalcogenides for Thermoelectric Applications.

A simple and effective preparation of solution-processed chalcogenide thermoelectric materials is described. First, PbTe, PbSe, and SnSe were prepared by gram-scale colloidal synthesis relying on the reaction between metal acetates and diphenyl dichalcogenides in hexadecylamine solvent. The resultant phase-pure chalcogenides consist of highly crystalline and defect-free particles with distinct cubic-, tetrapod-, and rod-like morphologies. The powdered PbTe, PbSe, and SnSe products were subjected to densification by spark plasma sintering (SPS), affording dense pellets of the respective chalcogenides. Scanning electron microscopy shows that the SPS-derived pellets exhibit fine nano-/micro-structures dictated by the original morphology of the key constituting particles, while the powder X-ray diffraction and electron microscopy analyses confirm that the SPS-derived pellets are phase-pure materials, preserving the structure of the colloidal synthesis products. The resultant solution-processed PbTe, PbSe, and SnSe exhibit low thermal conductivity, which might be due to the enhanced phonon scattering developed over fine microstructures. For undoped -type PbTe and -type SnSe samples, an expected moderate thermoelectric performance is achieved. In contrast, an outstanding figure-of-merit of 0.73 at 673 K was achieved for undoped -type PbSe outperforming, the majority of the optimized PbSe-based thermoelectric materials. Overall, our findings facilitate the design of efficient solution-processed chalcogenide thermoelectrics.