High-performance half-Heusler thermoelectric devices through direct bonding technique

Abstract

Solid-state thermoelectric generators (TEGs) are promising solution for waste heat recovery. However, they typically suffer from lower conversion efficiency, lack of reliable high temperature device fabrication process and long-term stability. In order to realize high electrical conversion efficiency (ECE) in TEGs, it is critical that in conjunction with high TE materials figure of merit, zT, there is also a reliable TE module fabrication process. This study demonstrates the TEG fabrication process that results in reduced thermal and electrical contact resistances between metal electrodes and TE legs, even at high temperatures (>600 °C). The fabrication approach is demonstrated using p-type ZrCoSb-based and n-type ZrNiSn-based half-Heusler TE materials. High temperature brazing material is used as a filler that enables direct bonding of TE legs to the copper electrode without metallizing legs. This technique improves the TEG performance and stability at high temperatures by minimizing the contact resistance and diffusion at TE leg/electrode interface. The fabricated modules exhibit a high power density of ~11.5 Wcm−2 and an ECE of 9.5% at 670 °C temperature gradient. The module was exposed to longtime soaking at 550 °C in air and was found to exhibit negligible deterioration. These results are highly promising for advancing the TE modules in waste heat recovery applications.