Abstract

Bismuth telluride-based thermoelectric generators (TEG) were widely used in waste heat recovery, but the failure problem at the electrode interface was serious, which was related to the severe diffusion between Sn and Bi2Te3. However, the diffusion behavior and process have not been reasonably evaluated and mechanism analyzed, which was not conducive to the design and improvement of TEGs. In this work, hot-end electrode aging was performed at 150 °C, and the diffusion, intermetallic compounds (IMC), as well as crack induction between Bi2Te3 and Sn-based solder were systematically investigated. It was found that the interdiffusion of Sn and Te atoms led to the formation of Bi2Te with HCP structure and SnTe with FCC structure at the interface. Bi2Te was a Bi-rich layer formed after the migration of Te atoms away from Bi2Te3, and SnTe had a double-layer structure respectively attributing to the diffusion of Sn and Te atoms. Diffusion-induced cracks tended to occur at Bi2Te/SnTe interfaces and SnTe/Sn interfaces. The former was related to the diffusion-induced phase transformation at the diffusion front of Sn atoms, while the latter generated from the initiation and expansion of Kirkendall voids. In addition, the brittleness of the Bi-rich phase aggravated the crack propagation. The shear test results of the electrodes confirmed that these cracks were the weakness of TEG electrodes. It was recommended to introduce a barrier layer at the interface to provide protection, and the fabrication of direct soldering was not suggested.

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