Novel thermal generator works at room temperature
Researchers in Japan have developed a new type of organic thermoelectric device that can harvest energy from ambient temperature.
The team at Kyushu University succeeded in developing a thermal generator that works at room temperature without any temperature gradient.
Thermoelectric devices, or thermoelectric generators, are a series of energy-generating materials that can convert heat into electricity so long as there is a temperature gradient—where one side of the device is hot and the other side is cool. Such devices have been a significant focus of research and development for their potential utility in harvesting waste heat from other energy-generating methods.
The organic thermoelectric device has a new power generation mechanism that extracts small-scale thermal energy, a few tens of millielectronvolts, at room temperature without a temperature gradient says the paper in Nature Communications.
The device is based on interfaces composed of copper phthalocyanine and copper hexadecafluoro-phthalocyanine as the donor and acceptor, producing an open-circuit voltage VOC of 384 mV, short-circuit current density JSC of 1.1 μA/cm2, and maximum output Pmax of 94 nW/cm2 are obtained at room temperature without the use of a temperature gradient.
The temperature characteristics of the thermoelectric properties yield activation energy values of approximately 20–60 meV, confirming the low-level thermal energy’s contribution to the power generation mechanism.
“We were investigating ways to make a thermoelectric device that could harvest energy from ambient temperature. Our lab focuses on the utility and application of organic compounds, and many organic compounds have unique properties where they can easily transfer energy between each other,” said Professor Chihaya Adachi of Kyushu University’s Centre for Organic Photonics and Electronics Research (OPERA) who led the study. “A good example of the power of organic compounds can be found in OLEDs or organic solar cells.”
The key was to find compounds that work well as charge transfer interfaces, meaning that they can easily transfer electrons between each other. After testing various materials, the team found two viable compounds: copper phthalocyanine (CuPc) and copper hexadecafluoro phthalocyanine (F16CuPc).
“To improve the thermoelectric property of this new interface, we also incorporated fullerenes and BCP,” said Adachi. “These are known to be good facilitators of electron transport. Adding these compounds together significantly enhanced the device’s power. In the end, we had an optimized device with a 180 nm layer of CuPc, 320 nm of F16CuPc, 20 nm of fullerene, and 20 nm of BCP.”
“There have been considerable advances in the development of thermoelectric devices, and our new proposed organic device will certainly help move things forward,” concludes Adachi. “We would like to continue working on this new device and see if we can optimize it further with different materials. We can even likely achieve a higher current density if we increase the device’s area, which is unusual even for organic materials. It just goes to show you that organic materials hold amazing potential.”
doi.org/10.1038/s41467-024-52047-5
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