Low Frequency Impedance Spectroscopy Analysis of Thermoelectric Modules

Abstract

Impedance spectroscopy is a well-established technique for the study of semiconductors and energy-related devices. However, in the area of thermo- electrics (TEs), this technique is not frequently used and there is a lack of a physical background for a proper interpretation of the results. Usually, in the low frequency regime, the impedance spectrum of TE modules working in cooling mode is characterized by a semicircle which can be modelled as a parallel connection of a resistor and a capacitor. Here, we present a theoretical analysis to understand the origin of both parameters in bulk TE modules working as Peltier coolers. The analysis introduces a thermoelectric capaci- tance and a thermoelectric resistance that are defined by the temperature, the Seebeck coefficient and the thermal properties of the module (specific heat and thermal conductivity, respectively). The product of both provides a time con- stant that directly relates to the thermal diffusivity. Our analysis provides a theoretical model able to interpret the low frequency results and obtain rele- vant thermal parameters from a single impedance measurement.