Cost Efficient Manufacturing of Silicide Thermoelectric Materials and Modules using RGS Technique

Thermoelectric (TE) power generation presents a promising and attractive way to convert high temperature waste heat into electricity. However in many situations, such as in industrial waste heat recovery, the market is looking for affordable solutions, while the search for efficient and stable materials is still ongoing. The relatively high TE system costs, are partially due to material costs such as for Te in BiTe, or PbTe, but also due to the relatively small scale leg-and module manufacturing process. Especially in the leg manufacturing, there are often a number of steps involved such as ingot crystallization, ball milling, hot pressing or plasma sintering and leg sawing. With the availability of the ribbon-growth-on-substrate (RGS) technology, it is possible to cast semiconductor material in a net-shape form directly from the melt, thus reducing the number of manufacturing steps, material losses and production costs. In combination with a strip leg based module concept, the potential for a major cost reduction step is within reach. Besides affordability, other challenges are to demonstrate a material that is stable at elevated temperatures, and comparable or better than material produced by other semiconductor manufacturing processes. In this paper, the progress in manufacturing higher manganese silicon material by the RGS process is shown, demonstrating ZT values above 0.5. It could be shown that the phase composition can be controlled by the RGS process and that phase geometry is tunable by changing crystallization velocity. This phase structuring ability is seen as an opportunity to enhance phonon scattering by phase boundaries, and hence further improve ZT values. Controlling the Si phase in HMS was found to be key in the RGS material development process. Especially the addition of chromium doping not only changed carrier concentration and conductivity, but also resulted in a different phase composition of the cast material. In addition to the material development the strip material based module concept is introduced and first demonstrators devices are shown. (C) 2015 Published by Elsevier Ltd.