*3.7. E*ff*ect of Soldering Layers*

Table 6 shows the effect of soldering layers on maximum power, maximum efficiency, and maximum thermal stress of the thermoelectric module. For the same range of operating

temperature difference, the Bi2Te<sup>3</sup> material showed higher thermal stress compared to the SiGe material. Hence, soldering layers were only provided on the thermoelectric legs constructed with the Bi2Te<sup>3</sup> material [4]. In order to investigate the effect of the soldering layers, the single stage arrangement of the thermoelectric module with the square prism legs and the Bi2Te<sup>3</sup> material as well as the two-stage arrangement of the thermoelectric module with the square prism legs and the Bi2Te<sup>3</sup> material are compared with and without soldering layers. In addition, the two-stage arrangement with square prism legs with the SiGe+Bi2Te<sup>3</sup> material is also compared with and without soldering layers. In the case of the SiGe+Bi2Te<sup>3</sup> material with the soldering layers, the second stage of the Bi2Te<sup>3</sup> material is provided with soldering layers. Addition of the soldering layers reduces the thermal stress compared to the corresponding same configuration without soldering layers. The soldering layers experience most of the deformation compared to the other parts of the thermoelectric module and sometimes undergo plastic deformation. Hence, excessive thermal stress on the thermoelectric legs are reduced because the larger effect of the thermal stress is absorbed by the soldering layers. The thickness of the soldering layers is very small; hence, the resistance offered is a small contribution to the total effective resistance of the thermoelectric module. Therefore, the soldering layers have no significant effect on maximum power or maximum efficiency. The melting point temperature of the soldering layers is 185 ◦C; hence, various configurations of the thermoelectric module with soldering layers are operated at a maximum hot junction temperature below 185 ◦C. Therefore, a comparison of configurations of the thermoelectric module provided with and without soldering layers was done for temperature difference of 150 ◦C. Maximum stress for the various configurations with the soldering layers were considered only for the thermoelectric legs, not the entire thermoelectric module, as is shown in Table 6.


**Table 6.** Effect of soldering layers on various performance parameters.

SL means soldering layer.
