Scientists are getting closer to designing thermoelectric materials that efficiently harvest heat from the surrounding
environment and convert it into electricity to power various devices and appliances, according to a review of the latest
research in the journal Science and Technology of Advanced Materials. Devices made with these materials could avoid the
need to recharge, change and dispose of batteries.
For thermoelectric materials to be efficient energy producers, they need to be able to hold heat and conduct electricity
well. Thermoelectric materials that can work near room temperature and are flexible would be especially advantageous,
particularly for use in wearable devices.
Three types of conducting materials are being investigated for use in thermoelectric devices: inorganic, organic and
hybrid materials.
Inorganic thermoelectric materials efficiently convert heat into electricity, but are not very flexible. Researchers are
working to overcome this hurdle. For example, a flexible thermoelectric device was fabricated using chromel (90% nickel
and 10% chromium) and constantan (55% copper and 45% nickel) layers covered by a flexible sheet made of polyimide and
copper. Micro-thermoelectric generators based on inorganic materials have potential applications in environmental and
building monitoring, animal tracking, security and surveillance, and medical treatment. They have already been
introduced into commercial devices, such as a body-heat-powered watch manufactured by Seiko.
Most organic thermoelectric devices involve polymers. Semiconducting polymers conduct electricity and hold heat better
than conventional inorganic semiconductors. They are also lighter and less expensive. Unlike rigid inorganic materials,
they are flexible and moldable and can be produced in any shape using 3D printers. However, they are less efficient at
converting heat into electricity. Researchers are trying to improve the thermoelectric efficiency of polymers by tuning
the composition, length and arrangement of their molecules, aiming to increase the electrical conductivity and
crystallinity of the final material.
Research that aims to combine the advantages of organic and inorganic materials by blending them together is focused on
finding optimal compositions and improving the mixing process. For example, embedding organic molecules into inorganic
titanium disulfide crystals makes them flexible and reduces their thermal conductivity. This improves the overall
thermoelectric performance.
The authors conclude that thermoelectric devices can potentially replace traditional batteries in many applications, but
a lot of work on improving thermoelectric materials is required for achieving success in this direction.