Improved contact performance and thermal stability of Co–Ni alloy barrier layer for bismuth telluride-based thermoelectric devices

As a crucial material that connects the electrodes with the thermoelectric materials, barrier layer holds significant sway over the thermoelectric conversion efficiency and the stability of the thermoelectric device. However, the interfacial reaction between the Ni metal barrier layer and the thermoelectric materials in commercial Bi₂Te₃-based devices is detrimental to the device performance. In this work, a chemical electroplating process was employed to fabricate Co–Ni alloy barrier layers for Bi₂Te₃-based thermoelectric devices. The effect of different Co content on the phase composition, microstructure, and contact performance of the barrier layers were studied. The results suggest that Co–Ni alloy barrier layers can be formed by chemical electroplating process under the optimal condition although the addition of Co results in lowered electroplating rate and thinner barrier layers. It is beneficial that Co could effectively suppress the interface reaction between Ni and Bi₂Te₃-based materials, thereby inhibiting the formation of the NiTe or CoTe phase. Consequently, the Co20Ni80 alloy barrier layer exhibits a low contact resistance around 3 μΩ cm², an improved bonding strength of 9.6 MPa, as well as improved thermal stability. This work introduces a reliable strategy for improving the stability and lifespan of commercial Bi₂Te₃-based TE devices.