Interfacial evolution behavior of AgSbTe_2.01/nanosilver/Cu thermoelectric joints

Highlights: • Fine connection between AgSbTe_2.01 and copper electrode was made. • 316 stainless steel was a valid diffusion barrier layer in thermoelectric device. • FeTe₂ compounds were formed at AgSbTe_2.01/316 stainless steel interface. • CuO formed at Ag/Cu interface led to the failure of the whole joints. For high conversion efficiency thermoelectric generators, the preparation of fine and stable junctions between thermoelectric (TE) materials and electrodes is one of the core issues. In this paper, TE material AgSbTe_2.01 applied in medium temperature (200–400 °C) was successfully connected to copper electrode by low-temperature joining technique with nanosilver paste. 316 stainless steel was sputtered on the surface of TE material as the diffusion barrier layer. To investigate the interfacial evolution behavior, joints suffered from a bulk of harsh aging treatments under 200 °C to 400 °C in air environment. The results proved that 316 stainless steel could effectively block the diffusion between thermoelectric elements and element Ag in the solder at 200 °C to 400 °C. The formation of FeTe₂ at AgSbTe_2.01/316 stainless steel interface realized a fine metallurgical interconnection which was benefit for the improvement of joint strength. However, the mismatch of crystal structure between FeTe₂ and AgSbTe_2.01 might lead to defects under harsh environment. It was also concluded that the failure at Ag/Cu interface caused by the formation of CuO would be the main reason for the failure of the whole junction.