Interface Engineering Boosting High Power Density and Conversion Efficiency in Mg2Sn0.75Ge0.25‐Based Thermoelectric Devices

Abstract Electrode contact interfaces for practical thermoelectric (TE) devices require high bonding strength, low specific contact resistivity, and superb stability. Herein, the state‐of‐the‐art Cu 2 MgFe/Mg 2 Sn 0.75 Ge 0.25 interface is designed for Mg 2 Sn 0.75 Ge 0.25 ‐based TE devices, adhering to the general strategy of high bonding propensity, thermal expansion matching, diffusion passivation, and dopant inactivation. The interfacial stability is verified by the in situ transmission electron microscopy analysis, thereby confirming the contributions from decreasing the chemical potential gradient and increasing the diffusion activation energy barrier. The single‐leg device exhibits a high power density ( ω max ) of 2.6 W cm −2 and conversion efficiency ( η max ) of 8% under a temperature difference (Δ T ) of 370 °C, which is the record‐breaking value in comparison to other Mg 2 (Si, Ge, Sn)‐based TE devices. Additionally, a two‐couple device with p ‐type Bi 2 Te 3 shows an excellent ω max of 1.3 W cm −2 and η max of 5.4% under a Δ T of 270 °C, comparable to commercial Bi 2 Te 3 devices. The proposed interface design strategy provides a general technique for constructing high‐performance devices using cutting‐edge TE materials.