Effect of Electrical Contact Resistance on the Performance of Cascade Thermoelectric Coolers

Performance of low-temperature cascade thermoelectric coolers (TECs) is analyzed with emphasis on the deterioration of electrical contact resistance. Two key characteristics are under consideration: the maximum coefficient of performance at a given temperature difference and the maximum obtainable cooling for the TECs with fixed configuration. The deterioration of these characteristics with increasing of the resistance of electrical contacts is analyzed for the TECs having from two to six stages that are optimized to achieve the temperature differences of 100–150 K with minimal power consumption. The quality of electrical contacts is a crucial factor that greatly affects the performance of the cascade TECs. To maintain the TEC efficiency at an acceptable level, a contact resistance rc in the range from 10−7 Ω cm2 to 10−6 Ω cm2 should be provided, whereas with greater resistance, the TEC performance decreases dramatically, especially for the TECs with thermoelectric (TE) leg height of 0.5 mm and less. The irreversible losses caused by the resistance of the connecting metal strips are analyzed and the thicknesses that should provide an acceptably low rc level are determined for different cascade TECs with typical TE leg dimensions and spacing.