Development and evaluation of 3-stage segmented thermoelectric elements

One of a way to achieve high power performance of a thermoelectric device is to broaden the operating temperature range of thermoelectric materials. In order to realize this, a project team has carried out a cooperation research and we have developed 3-stage segmented thermoelectric elements. The element is composed of three kind of optimized thermoelectric materials: SiGe, PbTe and Bi2Te3. The segmented element can work at a wide range from room temperature to 1073 K. Every stage of the thermoelectric element was prepared both in monolithic and 2 layer-stepwise structure, and we simply called the 3-stage element constructed by gradient thermoelectric materials as FGM (functionally graded materials). For confirming the effect of large temperature range of the 3-stage segmented element, we also prepared standard monolithic SiGe element, which was machined as same size as the segmented one. Evaluations for every element included electric resistance, generative current, and power output. A large-temperature-span apparatus conducted the performance evaluations, and a high accuracy electronic load was used in this experiment. The results indicate that highest efficiency up to 17% is possible for the 3-stage segmented element, which was constructed by monolithic SiGe, PbTe and Bi2Te3. Amount of total resistively in the 3-stage segmented element extremely affects the power output. Improvement of joining process for a stepwise graded element will greatly contribute to high power performance.