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Probing of Thermal Transport in PbTe Nanocrystal Film by Time-Domain Thermoreflectance

Bottom-up fabrication of thermoelectric (TE) materials from colloidal nanocrystal (NC) building blocks can substantially increase their TE efficiency, e.g., by reducing lattice thermal conductivity. In this work, we first synthesized 10-nm spherical phase-pure oleate-capped PbTe NCs with narrow size distribution and employed them to fabricate the 110-nm thick films on insulating SiO2/Si substrates. Here, we used the spin-coating with subsequent ligand exchange procedure to ensure strong coupling interactions between the NCs. Using the dark conductivity measurements, we confirmed the semiconducting behavior and the Schottky-type electrical field-dependent conductivity mechanism in the resultant thin films. We then probed the thermal transport in the thin-film by means of a time-domain thermoreflectance (TDTR) method. For this purpose, we used a customized state-of-the-art system based on a picosecond thermoreflectance instrument, which enables area-selective analysis with the spatial resolution down to 5 m. The results show that as-fabricated PbTe NC films exhibit ultralow thermal conductivity of ca. 1.52 W m–1 K–1. All in all, the transport properties findings suggest potential of the proposed quick and cost-effective spin-coating strategy for bottom-up fabrication of nanostructured TE films from high-quality colloidal NC building blocks.