Overcoming Asymmetric Contact Resistances in Al-Contacted Mg2(Si,Sn) Thermoelectric Legs

Abstract

Thermoelectric generators are a reliable and environmentally friendly source of electrical energy. A crucial step for their development is the maximization of their efficiency. The efficiency of a TEG is inversely related to its electrical contact resistance, which it is therefore essential to minimize. In this paper, we investigate the contacting of an Al electrode on Mg2(Si,Sn) thermoelectric material and find that samples can show highly asymmetric electrical contact resistivities on both sides of a leg (e.g., 10 µΩ·cm2 and 200 µΩ·cm2). Differential contacting experiments allow one to identify the oxide layer on the Al foil as well as the dicing of the pellets into legs are identified as the main origins of this behavior. In order to avoid any oxidation of the foil, a thin layer of Zn is sputtered after etching the Al surface; this method proves itself effective in keeping the contact resistivities of both interfaces equally low (<10 µΩ·cm2) after dicing. A slight gradient is observed in the n-type leg’s Seebeck coefficient after the contacting with the Zn-coated electrode and the role of Zn in this change is confirmed by comparing the experimental results to hybrid-density functional calculations of Zn point defects.

High-Performance Functionalized Mg2Si0.9Sn0.1 Thermoelectric Leg Synthesis by a Single-Step Reactive SPS Process

“…Table shows the processing techniques and temperatures used in the literature to fabricate n-type Mg 2 (Si,Sn) with contacts. It has been reported that in n-type Mg 2 (Si,Sn) TE element fabrication, the material synthesis was carried out first and then separate contact fabrication processes were performed separately. ,,,− In addition, the contact layer oxidation and removal process are inevitable due to two different processing sequences, adding additional manufacturing costs for device fabrication.…”

“…In general, the underlying scientific principles for properly selecting contact materials and developing bonding techniques are still limited. Several elemental metallic contacts, such as Cu, ,, Ag, ,, Ni, ,,, and Al, − have been tried to achieve chemically and thermally stable joints on binary magnesium–silicon using different processing techniques. Few reported studies emphasized the use of binary ,, and ternary compounds to overcome the chemical reactivity of elemental metallic contacts.…”

“…31 However, the asymmetry in electrical contact resistances due to Al 2 O 3 layer formation is a significant concern in TEG performance. 30,32 Generally, the studies on Mg 2 Si 1−x Sn x materials suggested that the specific contact resistance (r c ) ≤ 10 μΩ cm 2 would be the benchmark value for high-power output. 12,19 However, the development of a low contact resistance between the thermoelectric material and the electrode is complicated due to the unstable chemical stoichiometric and pyrophoric nature of the main constituent element Mg.…”

“…Although several efforts have been made on contact making, it was found that the long processing time and high rate of diffusion kinetics lead to higher contact resistance and deterioration of properties of thermoelectric compounds. ,, Recently, aluminum contact fabrication on the Mg 2 (Si,Sn) material reported low contact resistance and high stability . However, the asymmetry in electrical contact resistances due to Al 2 O 3 layer formation is a significant concern in TEG performance. , …”

An Electrical Contacts Study for Tetrahedrite-Based Thermoelectric Generators

“…In the present work, contact resistances as low as ~43–59 mΩ.mm 2 were obtained in tetrahedrite legs/copper junctions. These values are close to the range reported for commercial TE devices (typically from 0.075 to 3.7 mΩ.mm 2 ) [ 51 , 52 , 53 ] and to other TE materials currently being studied, such as the skutterudites (~10–12 mΩ.mm 2 ) [ 54 ], the CoSb 3 compounds (~ 15 mΩ.mm 2 ) [ 55 ], and the Mg 2 (Si,Sn) legs (~1–20 mΩ.mm 2 ) [ 56 , 57 ].…”