Thermoelectric Cooler Prototype Based on Bismuth Telluride and Aimed for Space Applications

Sammanfattning: The main goal for this project was to design, manufacture and evaluate a thermoelectric cooler, TEC, prototype. One of the biggest challenges with TECs is that they need to be very reliable and have a long lifetime. The two biggest contributing factors to degradation and breakdown stem from thermal expansion mismatch, resulting in cracks, and from material diffusion between the thermoelectric material and connecting materials. The thermoelectric material in this case is Bismuth telluride, Bi2Te3, obtained from two suppliers. The thermoelectric cooler prototype was successfully manufactured. The prototype, which consisted of 38 thermoelectric elements, showed a maximum temperature difference of 65.1 degrees Celsius. A commercial TEC of the same size had a maximum temperature difference of 68 degrees Celsius. The figure of merit and grain size of p- and n-doped Bismuth Telluride from two different suppliers have been measured as means of testing the thermoelectric material prior to manufacturing, and to compare the suppliers. In this report, the figure of merit is a measure of how well a material converts electrical current to a heat gradient. The figure of merit for bismuth telluride, Bi2Te3, from both suppliers was found to be between 0.4 and 0.8 through the Harman method. Since studies show that smaller grains for Bi2Te3 result in a more durable material, the morphology was investigated. However, no grains could be observed with light optical microscopy with an applied etchant, or scanning electron microscopy. A cohesion tape test showed that Bismuth telluride from one of the suppliers is more fragile than the other.