Unified contact layer and low-temperature transient liquid phase interconnection for high-performance all-Mg-based thermoelectric devices.

Thermoelectric technology enables direct conversion of untapped low-grade waste heat into electrical energy. Mg₃(Sb, Bi)₂ and MgAgSb, with their excellent thermoelectric performance near room temperature, have emerged as cost-effective and environmentally friendly alternatives to Bi₂Te₃-based materials. However, the development of high-performance Mg-based thermoelectric devices faces significant challenges due to the inherent high chemical reactivity and volatility of Mg elements, coupled with the phase transition-induced degradation of thermoelectric properties in MgAgSb, which collectively led to poor interfacial contacts and device integration. In this study, a Mg-based thermoelectric device consisting of n-type Mg₃(Sb, Bi)₂ and p-type MgAgSb has been fabricated with Mg₂Ni as the unified contact layer for both materials. The Ni-Sn transient liquid-phase (TLP) low-temperature bonding technology has been employed for the integration of the thermoelectric device. In addition, thermal aging and cycling tests confirmed the long-term stability of the Mg₂Ni/TE contact interfaces and the Ni-Sn intermetallic compound (IMC) joints. Notably, the device with segmented n-type legs achieves an exceptional conversion efficiency of ∼10.8% at a temperature difference of 300 K. This work promotes the application of high-performance, environmentally friendly Mg-based thermoelectric devices in low-grade waste heat recovery.