On the electrophoretic deposition of Bi2Te3 nanoparticles through electrolyte optimization and substrate design

Abstract

Assembly of thermoelectric nanostructures with pre-defined morphology and surface chemistry on solid substrates has been one of the challenges for in-plane TE devices. Electrophoretic deposition (EPD) has the potential to be used for this purpose, where the use of non-conductive substrates is required to enable a reliable evaluation of the transport property of electrically active films. Bi2Te3 nanoparticles, which were synthesized using microwave-assisted hydrothermal route, were used for the EPD of thermoelectric films on glass substrates. A special substrate was fabricated using maskless photolithography, to evaluate the electronic transport properties of the TE films without the interference of the substrate. Electrolyte composition was optimized for high mobility of the suspended nanoparticles, and Bi2Te3 EPD films were fabricated with a high deposition rate, reaching 10 μm/min. Initial EPD films showed high resistivity, ascribed to the surface oxide layer and capping ligands. The resistance was significantly reduced by the addition of a dithiol molecular linker, capable of interconnecting the Bi2Te3 nanoparticles through ligand-exchange. Seebeck coefficient in the range −150 to −180 μV/K was measured, revealing the transport through the deposited films. Finally, a power factor of 169 nW/K2.m was estimated, revealing the potential for the application of this technology to large area TE films as active coatings using the developed EPD process.