Impedance spectroscopy-based electrical equivalent model of a thermoelectric module for the figure of merit (ZT)

Abstract

Impedance spectroscopy is able to simultaneously extract three key parameters, namely, the Seebeck coefficient, electrical conductivity, and thermal conductivity, leading to determination of the figure of merit (ZT). As the measurement method is simple, it can be used conveniently at room temperature. However, when measuring at high temperatures, there are restrictions on the IS method. Electrical parasitic parameters between the measuring equipment and the temperature chamber may reduce the reliability of the characterization. Since the electrical part connecting the temperature-variable chamber to the measuring equipment can have tens to hundreds of milliohms, it should be considered as lumped parameters in order to evaluate the intrinsic component of the thermoelectric module. In this study, the electrical and thermal characteristics of the Bi2Te3 thermoelectric module were evaluated in the range from room temperature to 150 ℃ using an impedance spectroscopy-based electrical equivalent model (ISEEM). The ISEEM includes an impedance component consisting of the thermoelectric module itself and the parasitic electrical impedance constituting the measuring apparatus, where the electrical impedance of the measuring equipment can be evaluated by the de-embedding method. As a result, it is possible to accurately extract the intrinsic characteristics of the Bi2Te3 thermoelectric module through ISEEM. The intrinsic parameters of a commercial thermoelectric module of 40 mm by 40 mm were obtained within an error rate of 5% regardless of the peripheral measuring device. Consequently, the module had a ZT maximum value of 0.73 at 22 °C and a performance of 0.49 at 150 °C. These results demonstrate that electrical and thermal characterization can be performed easily, and at the same time, the reliability of the characterization can be improved.