Thermoelectric material converts waste heat into electricity

A thermoelectric material developed in Saudi Arabia captures the heat lost by machines and devices and turn it back into electricity.

thermoelectric material
Mohamad Nugraha (left) and his group leader, Derya Baran, demonstrate the flexibility of the device (© 2019 KAUST)

The nanomaterial from KAUST (King Abdullah University of Science and Technology) is made using a low-temperature solution-based production process.

“Among the many renewable energy sources, waste heat has not been widely considered,” said 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.

Until now, thermoelectric materials have been made using expensive and energy-intensive processes. Baran, Nugraha and their colleagues have developed a new thermoelectric material made by spin coating a liquid solution of quantum dots.

The team spin coated a thin layer of lead-sulphide quantum dots on a surface and then added a solution of short linker ligands that crosslink the quantum dots together to enhance the material’s electronic properties.

After repeating the spin-coating process layer-by-layer to form a 200nm thick film, gentle thermal annealing dried the film and completed fabrication.

“Thermoelectric research has focused on materials processed at very high temperatures, above 400 degrees Celsius,” Nugraha said in a statement. The quantum-dot-based thermoelectric material is only heated up to 175 degrees Celsius. This lower processing temperature could cut production costs and means that thermoelectric devices could be formed on a broad range of surfaces, including cheap flexible plastics.

According to KAUST, the team’s material showed promising thermoelectric properties. One important parameter of a good thermoelectric is the Seebeck coefficient, which corresponds to the voltage generated when a temperature gradient is applied. “We found some key factors leading to the enhanced Seebeck coefficient in our materials,” Nugraha said.

The team was also able to show that an effect called the quantum confinement, which alters a material’s electronic properties when it is shrunk to the nanoscale, was important for enhancing the Seebeck coefficient. The discovery is a step toward practical high-performance, low-temperature, solution-processed thermoelectric generators, Nugraha said.

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