Interfacial Design Contributing to High Conversion Efficiency in Mg₃(Sb, Bi)₂/Bi₂Te₃ Thermoelectric Module with Superior Stability

Mg₃(Sb, Bi)₂-based materials possess excellent room-temperature thermoelectric performance, while poor interfacial behaviors occur when connected with metal electrodes due to the strong chemical activity and volatility of Mg element. In this study, a high efficiency of 7.1% under a temperature difference of 230 K is achieved in n-Mg₃(Sb, Bi)₂/p-Bi₂Te₃ thermoelectric module. When changing the interfacial layer from Fe powder to Fe foil, it effectively prevents a significant diffusion of both Mg and Bi elements from the material matrix to the interfacial layer, resulting in an extremely low contact resistivity ≈3.4 µΩ cm² that is almost one order lower than of that of Fe powder/Mg₃(Sb, Bi)₂ junction ≈30 µΩ cm². Particularly, a thin diffusion layer with a width of ≈2 µm is initially observed in the unannealed Fe foil/Mg₃(Sb, Bi)₂ junction. Even after thermal aging at 573 K for 28 days, the diffusion-layer width is basically unchanged and its corresponding contact resistivity maintained as low as ≈5.8 µΩ cm². Overall, this work provides deep insights into interfacial design and paves the way for high-performance and sustainable low-grade waste heat recovery.