Bismuth telluride (Bi2Te3) is one of the most widely studied and used thermoelectric materials. Since thermoelectric thin films have better properties than bulk ones, fabrication and characterization of thermoelectric thin films have become a key subject in the field of thermoelectric materials in recent years. In this thesis, Bi2Te3 films with two-dimensional and three-dimensional structures were successfully prepared by electrodeposition on conductive polyaniline (cPANI) substrate. The variation of electric conductivity of cPANI films with temperature and the influence of deposition parameters on composition, microstructure and properties of the as-deposited films have been systematically studied. The effects of macrostructure and the substrates on the Seebeck coefficient of Bi2Te3 film were also explored. The main results obtained are as follows:
It is revealed that the conductivity of the cPANI is affected by temperature and atmosphere during heat treatment. The electric conductivity of the cPANI films changed from 57S/cm to 0 and15S/cm, respectively, when the films were heat-treated at453K in nitrogen and argon for 3h.
The potential range for deposition of Bi2Te3 on the cPANI electrode was between -125 mV and -340 mV based on the cyclic voltammetry (CV) measurement. The deposition potential greatly influenced not only the Te content in Bi2Te3 films, but also the structure and Seebeck coefficient of the deposited layers, and Te content reached the minimum when -200mV was applied.
Investigation on the thermoelectric properties of the as-deposited Bi2Te3 thin films indicates: (1) The Seebeck coefficient of the alloy thin film was much improved after the insulation treatment because the substrate’s shunting action was eliminated. (2)Foam Bi2Te3 thin films exhibited much larger Seebeck coefficients than their bulk counterparts. (3)The Seebeck coefficients of foam Bi2Te3 alloys fabricated on phenolic resin and silicon carbide substrates with the same volume fraction and pore size are 64.7% and 145% higher than that of planar films respectively. We supposed that the influence of substrate on the Seebeck coefficient may be ascribed to the stress developed between the substrate and the deposited film.
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