Phase penetration: key drivers in barrier layer failure of Hf-free Half-Heusler thermoelectric modules

The high-temperature interfacial diffusion in Half-Heusler devices represents substantial challenges for practical applications. Especially, the diffusion of Ag from the conventional solder potentially leads to a decline in material performance and impacts device stability. In this study, the anomalous diffusion of Ag through the barrier into the material was revealed when Cr powder barrier layer was used for Ti0.5Zr0.5NiSn0.98Sb0.02. In contrast, Cr foil was employed to pre-densify and effectively prevent Sn phase penetration, thereby eliminating diffusion pathways for Ag and protecting against property degradation. After aging at 973 K for 30 days, the junction maintained a clean interface, exhibiting a low contact resistivity of 0.27 μΩ cm2. Benefiting from interfacial design, a high efficiency of 10.4% at the hot-side temperature of 976 K is achieved in the Hf-free Half-Heusler module, together with long-term good stability. This work addressed the remaining bottlenecks of the development of high-performance and low-cost Half-Heusler modules, facilitating the commercial application of Half-Heusler modules.