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

Abstract 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.