This Thermoelectric Generator Harvests Energy at Room Temperature — No "Cold Side" Required

Researchers from Kyushu University, the Materials Open Laboratory (MOL), the Institut Parisien de Chimie Moléculaire (IPCM), and GCE Institute Inc. have designed an organic thermoelectric device that, they say, is able to harvest power at room temperatures — even without a temperature gradient.

"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," explains Chihaya Adachi, a professor at Kyushu University's Center for Organic Photonics and Electronics Research (OPERA) and leader of the study. "A good example of the power of organic compounds can be found in OLEDs or organic solar cells."

A traditional thermoelectric energy harvester works by taking advantage of a temperature gradient: the difference in temperature between the "cold side" of the device and the "hot side." This requires both a source of heat and a method of cooling the device — and care must be taken that you're not consuming more energy to cool the generator than it's able to harvest.

The team's approach, though, aimed to turn heat into energy without the need for such a large difference in temperatures — delivering a device that operates even when the whole generator is at room temperature. Constructed from copper phthalocyanine (CuPc) and copper hexadecafluoro-phthalocyanine (F₁₆CuPc), with thin layers of fullerene and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), the gadget could be used in areas where traditional thermoelectric generator simply won't operate.

In testing, the prototype device showed an open-circuit voltage measured at 384mV, a short-circuit current density of 1.1μA/cm², and a maximum output of 94nW/cm² — and while an output of measured in nanowatts is quite some distance from what you'd need to power something like a smartphone, it's a starting point for potential optimization.

"There have been considerable advances in the development of thermoelectric devices, and our new proposed organic device will certainly help move things forward," says 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."

The team's work has been published in the journal Nature Communications under open-access terms.

Main article image courtesy of Chihaya Adachi/Kyushu University.