Abstract:To reduce consumption for ambient assisted living (AAL) applications, we propose the design and fabrication of flexible thin-film thermoelectric generators at a low manufacturing cost. The generators were fabricated using a combination of electrodeposition and transfer processes. N-type Bi 2 Te 3 films and p-type Sb 2 Te 3 films were formed on a stainless-steel substrate employing potentiostatic electrodeposition using a nitric acid-based bath, followed by a transfer process. Three types of flexible thin-film thermoelectric generators were fabricated. The open circuit voltage (V oc ) and maximum output power (P max ) were measured by applying a temperature difference between the ends of the generator. The thin-film generators obtained using thermoplastic sheets with epoxy resin exhibited a V oc that was tens of millivolts. In particular, the contact resistance of the thin-film generator decreased when silver paste was inserted at the junctions between the n-and p-type films. The most flexible thin-film generator fabricated in this study exhibited a P max of 10.4 nW at a temperature difference of 60 K. The current performance of the generators was too low, but we innovated a combination process to prepare them. It is expected to increase the performance by further decreasing the micro-cracks and contact resistance in the generators.

Please cite this article as: N. Hatsuta, D. Takemori, M. Takashiri, Effect of thermal annealing on the structural and thermoelectric properties of electrodeposited antimony telluride thin films, Journal of Alloys and Compounds (2016), ABSTRACTWe investigated the effect of thermal annealing on structural and thermoelectric properties of p-type antimony telluride (Sb 2 Te 3 ) thin films fabricated on a stainless steel (SUS304) substrate by electrodeposition. Antimony telluride thin films were annealed for 1 h at temperatures between 200 and 400°C. We observed that the as-deposited thin film and thin films annealed at temperatures less than 250°C possessed a stoichiometric atomic composition (Sb:Te = 40:60) with no impurities from the substrate. At the annealing temperature of 300°C, we observed a certain amount of impurities (Fe, Cr, Ni) in the thin film. The Seebeck coefficient was decreased but the electrical conductivity was increased for films treated at 300°C. As a result, the thin film exhibited a maximum power factor of 13.6 µW/(cm·K 2 ). On further increasing the annealing temperature to 400°C, the film structure and thermoelectric properties were drastically changed. The impurity concentration in the thin film reached approximately 50 at%. The crystal structure of Sb 2 Te 3 completely disappeared, and instead, other chemical compounds formed by alloying the elements of the thin film and the substrate were observed.

Bismuth telluride thin films were prepared on nickel plate by galvanostatic electrodeposition from hydrochloric acid-based electrolyte. It was found that the structural and thermoelectric properties of the thin films were strongly dependent on the Te content in the electrolyte. All thin films with various Te contents exhibited peaks in their X-ray diffraction patterns corresponding to the reflections of the rhombohedral phase of Bi2Te3. The surface morphology of the thin films with nearly stoichiometric composition was formed by dendritic crystallites, and that of the Te-rich thin film revealed a granular structure. The electrical conductivity of these thin films seemed to be influenced by both the Te content and the morphology. The Seebeck coefficient of the thin films exhibited both negative and positive values in dependence of the quantity of Te in the electrolyte. This behavior is advantageous because only by changing the Te content of the electrolyte, the material composition can be manipulated to yield either p-type or n-type semiconductors suitable for thermoelectric devices.

This paper describes the fabrication and characterization of bismuth telluride (Bi-Te), bismuth selenide (BiSe) and bismuth telluride selenium (Bi-Te-Se) thin films by electrodeposition. We examined the relationship between the mole ratio in the solution and the thermoelectric and structural properties of thin films. The thermoelectric properties, in terms of the electrical conductivity, Seebeck coefficient and power factor, were measured at room temperature. Then, the structural properties such as surface morphology and atomic composition were analyzed. The power factor of Bi-Te, Bi-Se and Bi-Te-Se thin films were achieved 3.1, 13.3 and 10.3 W/cm/K 2 , respectively. Although resulting performances were relatively high compared to those of thin films prepare using electrodeposition, there is still room for improvement to optimize the atomic composition of the thin films.

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