• • Cr foil barrier layer pre-densification suppresses Sn phase penetration, eliminating Ag diffusion pathways and maintaining a clean interface after aging at 973 K for 30 days, with contact resistivity as low as 0.27 μΩ cm2—critical for long-term device reliability.
• • The Hf-free Half-Heusler module achieves a conversion efficiency of 10.4% at a hot-side temperature of 976 K, demonstrating that cost reduction via Hf elimination does not compromise performance when interfacial design is optimized.
• • Anomalous Ag diffusion through Cr powder barrier layers is identified as a key failure mechanism, driven by Sn phase penetration—highlighting the necessity of barrier layer morphology control to prevent interfacial degradation.
• • The study provides a practical pathway to overcome the trade-off between material cost and device stability, enabling commercial deployment of Half-Heusler modules in mid-to-high temperature waste heat recovery.