Thermoelectric devices, often used to convert waste heat into electricity, have been primarily deployed in applications such as space probes. These systems rely on a temperature difference, often powered by radioisotopes in space missions like the Mars Curiosity rover and the Voyager probe. Despite their promise, challenges such as high cost, the use of hazardous materials, and low efficiency have limited widespread adoption.
"We were investigating ways to make a thermoelectric device that could harvest energy from ambient temperature," said Professor Chihaya Adachi of Kyushu University's Center for Organic Photonics and Electronics Research (OPERA). "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." Adachi noted that organic compounds have already proven useful in technologies like OLEDs and organic solar cells.
The team discovered that copper phthalocyanine (CuPc) and copper hexadecafluoro phthalocyanine (F16CuPc) were highly effective for electron transfer. To enhance the device's efficiency, they added fullerenes and BCP, compounds known for facilitating electron transport. This combination resulted in an optimized device with a layered structure: 180 nm of CuPc, 320 nm of F16CuPc, 20 nm of fullerene, and 20 nm of BCP.
"To improve the thermoelectric property of this new interface, we also incorporated fullerenes and BCP," Adachi added. "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."
The device achieved an open-circuit voltage of 384 mV, a short-circuit current density of 1.1 uA/cm, and a maximum power output of 94 nW/cm, all at room temperature without a temperature gradient.
"There have been considerable advances in the development of thermoelectric devices, and our new proposed organic device will certainly help move things forward," Adachi concluded. "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 that organic materials hold amazing potential."
Research Report:Organic Thermoelectric Device Utilizing Charge Transfer Interface as the Charge Generation by Harvesting Thermal Energy
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