New materials and devices for thermoelectric applications

The development of new, more efficient materials and devices is the key to expanding the range of application of thermoelectric generators and coolers. In the last couple of years, efforts to discover "breakthrough" thermoelectric materials have intensified, in particular in the U.S. Recent results on novel materials have already demonstrated that dimensionless figure of merit ZT values 40 to 50% larger than 1.0, the current limit, could be obtained in the 475 to 950K temperature range. New terrestrial power generation applications have been recently described in the literature. There exists a wide range of heat source temperatures for these applications, from low grade waste heat, at 325-350K, up to 850 to 1100K, such as in the heat recovery from a processing plant of combustible solid waste. The automobile industry has also recently developed a strong interest in a waste exhaust heat recovery power source operating in the 375-750K temperature range to supplement or replace the alternator and thus decrease fuel consumption. Based on results achieved to date at the Jet Propulsion Laboratory (JPL) on novel materials, the performance of an advanced segmented generator design operating in a large 300-945K temperature gradient is predicted to achieve about 15% conversion efficiency. This would be a very substantial improvement over state-of-the-art (SOA) thermoelectric power converters. Such a terrestrial power generator could be using waste heat or liquid fuels as a heat source. High performance radioisotope generators (RTG) are still of interest for deep space missions but the shift towards small, light spacecrafts has developed a need for advanced power sources in the watt to milliwatt range. The "powerstick" concept would provide a sturdy, compact, lightweight and low cost answer to this need. The development of thin film thermoelectric devices also offer attractive possibilities. The combination of semiconductor technology, thermoelectric films and high thermal conductivity materials could lead to the fabrication of light weight, high voltage devices with high cooling or high electrical power density characteristics. The use of microcoolers for the thermal management of power electronics is of particular interest.