Impedance spectroscopy for assessment of thermoelectric module properties under a practical operating temperature

Impedance spectroscopy has recently received considerable attention in terms of thermoelectric module characterization. However, to date, no study has been conducted on the high-temperature measurement of the module using impedance spectroscopy. In this paper, a systematic study on the Bi2Te3-based thermoelectric module up to 150 °C is reported. Evaluation results indicated that impedance spectroscopy could be used for characterizing the thermoelectric module in a practical operation temperature range. The impedance spectroscopy data of the module changed with the increased temperature on account of the change in the characteristics of the thermoelectric legs. Analysis of the impedance spectroscopy data enabled determination of the thermoelectric module figure of merit, while enabling extraction of three key parameters-the Seebeck coefficient, thermal conductivity, and electrical conductivity-by employing a one-dimensional heat equation. The results indicated that, while the thermal conductivity increased with temperature, the electrical conductivity decreased with increasing temperature. The Seebeck coefficient increased with temperature up to 100 °C and tended to be saturated. The module figure of merit was 0.82 and peaked at 75 °C. The results obtained in this study can contribute to the rapid evaluation of thermoelectric modules for exploiting various novel thermoelectric materials, metallization layers, electrodes, and insulating plates.