Thermoelectric Material Fabricated at Low Temperature
Researchers at King Abdullah University of Science and Technology (KAUST) say that some of the energy wasted as heat could be recaptured with an inexpensive thermoelectric nanomaterial that they developed. The researchers speculate that the thermoelectric nanomaterial could capture the heat from devices ranging from mobile phones to vehicle engines, and transform it directly into useful electricity.
They used a low-temperature solution-based production process to fabricate the nanomaterial, making it suitable for coating on flexible plastics.
"Among the many renewable energy sources, waste heat has not been widely considered," says Mohamad Nugraha, a postdoctoral researcher in Derya Baran's lab. Waste heat emitted by machines and devices could be recaptured by thermoelectric materials. These substances have a property that means that when one side of the material is hot and the other is cold, an electric charge builds up along the temperature gradient.
Previously, thermoelectric materials required expensive and energy-intensive processes. Baran, Nugraha and their collaborators have developed a new thermoelectric material that they made by spin coating a liquid solution of nanomaterial quantum dots.
The group spin coated a thin layer of lead-sulphide quantum dots on a surface. Then, they added a solution of short linker ligands that crosslink the quantum dots together to improve the material's electronic properties. Layer by layer they added to the surface repeating the spin coating process to form a 200-nanometer-thick film. A gentle thermal annealing process was then used to dry the film and complete the fabrication.
"Thermoelectric research has focused on materials processed at very high temperatures, above 400 degrees Celsius," Nugraha said.
The quantum-dot-based thermoelectric material is only heated up to 175°C. This lower processing temperature could reduce production costs, and, therefore, thermoelectric devices could be fabricated on a broad range of surfaces, including inexpensive and flexible plastics.
The team's material also showed encouraging thermoelectric properties. One critical parameter of a good thermoelectric is the Seebeck coefficient, which corresponds to the voltage produced when a temperature gradient is applied.
"We found some key factors leading to the enhanced Seebeck coefficient in our materials," Nugraha said.
The researchers also showed that an effect called the quantum confinement, which changes a material's electronic properties when it is shrunk to the nanoscale, was essential for enhancing the Seebeck coefficient.
According to Nugraha, the discovery is a step toward practical high-performance, low-temperature, solution-processed thermoelectric generators.
Nugraha, M.I., Kim, H., Sun, B., Haque, M.A., de Arquera, F.P.G., Villalva, D.R., El-Labban, A., Sargent, E.H., Alshareef, H.N. & Baran, D. Low-temperature-processed colloidal quantum dots as building blocks for thermoelectrics. Advanced Energy Materials 4, (2019). https://doi.org/10.1002/aenm.201803049