Self-optimized contact in air-robust thermoelectric junction towards long-lasting heat harvesting

Ensuring long-term reliable contacts in thermoelectric devices is particularly challenging due to their operation under high temperatures and has been one of the large obstacles in the field for application. Typically, thermodynamically driven atomic diffusion and reactions often degrade the contacts, leading to increased contact resistivity and ultimately limiting the device's lifespan. Here, we report an unconventional self-optimized contact resistivity mechanism in the Sb/MgAgSb junction. Mg diffusion from MgAgSb to Sb does not degrade but instead optimizes its contact resistivity even after aging in air for 30 days. This unexpected automatic optimization arises from an increased carrier concentration in MgAgSb, which enhances electron tunneling across the interface, effectively reducing the contact resistivity. Leveraging the self-optimized contact in Sb/MgAgSb and stable thermoelectric performance of MgAgSb, a two-pair thermoelectric device employing 100-day air-aged Sb/MgAgSb achieves an impressive conversion efficiency of 8.1% and a rare power density of 0.41 W cm^-2 under 294 K temperature gradient. These results underscore its significant potential for robust, long-term heat harvesting. The self-optimization mechanism identified in this work also offers valuable insights for designing future junctions for high-temperature applications.