Realizing 10% Conversion Efficiency by Contact Engineering of Mg₃Sb_1.5Bi_0.5 for Medium Temperature Thermoelectric Power Generation

Parasitic losses at various interfaces play a crucial role in determining the thermoelectric (TE) generator performance. In this work, we adopt an approach wherein the interface contact resistance can be minimized by using a combination of the multilayer (ML) contacting technique and transient liquid phase (TLP) bonding. The technique was experimentally verified with doped Mg₃Sb_1.5Bi_0.5. First, a contacted leg consisting of the TE material, the diffusion barrier layer, and an outer metallic (copper) layer was prepared by the ML process. This was then joined to a copper bridge (mimicked by copper holders) by using the TLP process with tin as the brazing element. Our contact resistance measurements indicate an extremely low value corresponding to 2.5% of the total resistance for the TLP-joined layer, which corresponds to a ∼2.6% lowering of the peak efficiency (η_max) value compared to that of an uncontacted leg. Thermoelectric generator (TEG) measurements were obtained for the contacted leg. The contacted leg exhibited an η_max value of ∼10% and a power output of 80 mW when it was subjected to a temperature gradient (ΔT) of 330 K. These results demonstrate that, by combining ML contacting with TLP bonding, interface contact engineering can be a potential method for enhancing TE performance.