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Thermoelectric Properties of Bismuth-Telluride Thin Films and Their Thermoelectric Generators
Masayuki Takashiri, Toshiteru Shirakawa, Koji Miyazaki, Hiroshi Tsukamoto

In this study, we fabricated bismuth-telluride thin films and their generators by using the flash evaporation method. We prepared fine powders of Bi2.0Te2.7Se0.3(n-type) and Bi0.4Te3.0Sb1.6 (p-type) by the centrifugal atomization method. The thermoelectric properties of as-grown thin films were lower than those of bulk materials. Therefore the as-grown thin films were annealed in hydrogen at atmospheric pressure for 1 hour in a temperature range of 200 to 400 °C. The grains grew to the same size as the film thickness at high annealing temperature. However, annealing at excessive high temperature caused the evaporation of tellurium. By optimizing the annealing temperature, thin films with high thermoelectric power factors of 8.8 µW/(cm ·K2) in n-type and 13.8 µW/(cm ·K2) in p-type were obtained. To evaluate the figure of merit of the thin film, the thermal conductivity of the n-type thin film was measured by the 3w method. The thin film annealed at 200 °C exhibited the cross-plane thermal conductivity of 1.2 W/(m.K). Mini-generators of flash-evaporated bismuth-telluride thin films were fabricated using shadow masks. The thin film thermoelectric generator with 7 pairs of p-n legs and aluminum electrodes was 20mm by 15mm size. The best generator was fabricated at annealing temperature of Ta =250 °C. The maximum voltage generated was 83.3 mV at a temperature difference of T = 30K.

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