Ni barrier in Bi2Te3-based thermoelectric modules for reduced contact resistance and enhanced power generation properties

Ni layer is widely utilized in Bi2Te3-based thermoelectric generators (TEGs) as a diffusion barrier layer. However, its influences on the contact resistance of the solder joints and the power generation properties of the TEGs are still unclear, which are of great importance in practical applications. In this study, Bi2Te3-based thermoelectric (TE) modules with Ni (NiTM) and without Ni (TM) layer were fabricated by using Sn96.5Ag3Cu0.5(SAC305) solder. Experimental results showed that Ni layer could effectively reduce 32% of contact resistances in P-type and N-type solder joints. P-type solder joint with Ni avoided voids forming on the border of the Bi0.5Sb1.5Te3 and SAC305 by suppressing severe Te and Sb elements diffusion. In N-type solder joint, since Ni inhibited the formation of Bi-Te self-diffusion barrier layer, no cracks generated at the interface between Bi2Te2.5Se0.5 and SAC305. In terms of power generation abilities, the inherently superior performance of TE legs was maintained due to effective suppression of element diffusion. When the temperature difference was 161 degrees C, the open circuit voltage of NiTM exhibited an enhancement of 13% compared with that of TM. The lower contact resistance and higher open circuit voltage resulted in a much higher maximum output power (an enhancement of 90%) in NiTM. (C) 2019 Elsevier B.V. All rights reserved.