New thermoelectric device collects energy at room temperature

Scientists at Kyushu University in Japan have designed a new organic device for harvesting energy at room temperature. This opens the door to building nontoxic, flexible, and even large-scale devices that could be powered by ambient temperatures in the future.

The technology is based on an older approach that even allowed the Voyager probe to draw power from an onboard device. Called thermoelectric generators, these devices can convert heat into electricity if they have a thermal gradient—one end of the material is hot and the other is cool.

This approach can also be used to harness waste heat and reuse it, making it a “hot” research and development topic. NASA even used a thermoelectric generator on its Curiosity rover that contained a radioactive isotope that generated heat. The gradient that was created was used to power onboard instruments.

But creating devices with radioactive isotopes for general use is expensive, inefficient, and even dangerous. So a research team led by Chihaya Adachi, a professor at Kyushu University, worked to develop a thermoelectric device that uses organic materials and operates at ambient temperature.

“Just as solar cells generate electric current by absorbing photons, the mechanism of this thermoelectric device generates electric current by absorbing phonons,” Adachi said. Interesting engineering in an email. A phonon is a quantum unit of vibration or sound.

How was the energy harvesting device built?

Scientists working at the University’s Organic Photonics and Electronics Research Center (OPERA) were inspired by organic LEDs and solar cells that use organic compounds.

In their application, the key was to find compounds that could act as a charge transfer interface. “The basic idea is to combine a donor molecule that can easily donate electrons with an acceptor molecule that has a strong ability to withdraw electrons,” Adachi explained in an email to TJ“There are only a limited number of acceptor materials that meet this requirement.”

After analyzing a database of more than 3,000 candidates, the team optimized the device design using copper phthalocyanine (CuPc) and copper hexadecafluorophthalocyanine (F16CuPc), and also incorporated fullerenes and BCP to improve the device’s thermoelectric properties.

“They are known to be good electron transport facilitators. Adding these compounds together significantly increased the power of the device,” Adachi said.

Device output

The researchers’ optimized device design included a 180 nm thick CuPc layer, a 320 nm thick F16CuPc layer, a 20 nm thick fullerene layer, and a 20 nm thick BCP layer.

“Although the role of fullerenes and BCPs is still unclear, I can say that they serve to extract electrons generated at the organic-CT interface with the electrode. These materials have relatively long electron diffusion coefficients and are widely used in organic solar cells,” Adachi said. TJ.

The device’s open-circuit voltage was 384 mV, and the short-circuit current density was 1.1 uA per square cm, with a maximum output power of 94 nW/square cm, the statement added. “The current value is less than microamps/square cm, but it is relatively easy to improve the current value by increasing the large area,” Adachi said. TJ.

The team will also work on optimizing the device using different materials.

The research results were published in Nature communication Today.