On the Challenges of Reducing Contact Resistances in Thermoelectric Generators Based on Half-Heusler Alloys

A method using fast hot pressing to join half-Heusler (HH) thermoelectric materials directly to an electrical current collector (Ag electrode) without using a third filler material is introduced. The compositions of the HH alloys used are Hf0.5Zr0.5CoSn0.2Sb0.8 and Ti0.6Hf0.4NiSn for p- and n-type, respectively. Using this method, the quality of the HH–electrode contacts is improved due to their low electrical contact resistance and less reaction–diffusion layer. The microstructure and chemical composition of the joints were examined using a scanning electron microscope equipped with energy-dispersive x-ray analysis. The electrical characteristics of the interfaces at the contacts were studied based on electrical contact resistance and Seebeck scanning microprobe measurements. In this paper, we show that joining the HH to a Ag electrode directly using fast hot pressing resulted in lower contact resistance and better performance compared with the method of using active brazing filler alloy.