The team at the US Department of Energy's National Renewable Energy Laboratory (NREL) worked with US smart material supplier International Thermodyne and researchers at the University of Denver used semiconducting single-walled carbon nanotubes (SWCNTs) as the primary material for efficient n- and p-type thermoelectric generators, rather than being used as a component in a "composite" thermoelectric material containing, for example, carbon nanotubes and a polymer.
"There are some inherent advantages to doing things this way," said Jeffrey Blackburn, a senior scientist in NREL's Chemical and Materials Science and Technology centre (above right). These can be processed in liquids that are lightweight and flexible and inexpensive to manufacture. This could be used to power more sophisticated electronics in smart fabrics such as sensors.
Removing polymers from all the SWCNT starting materials boosted the thermoelectric performance and lead to improvements in how charge carriers move through the semiconductor. The research also demonstrated that the same SWCNT thin film achieved identical performance when doped with either positive or negative charge carriers, which polymer-based systems struggle to do. These are needed to generate sufficient power in a thermoelectric device.
As SWCNT thin films can make p-type and n-type legs out of the same material with identical performance means that the electrical current in each leg is inherently balanced, which should simplify the fabrication of a device. The highest performing materials had performance metrics that exceed current state-of-the-art solution-processed semiconducting polymer organic thermoelectrics materials.
"We could actually fabricate the device from a single material," said fellow researcher Andrew Ferguson. "In traditional thermoelectric materials you have to take one piece that's p-type and one piece that's n-type and then assemble those into a device."