Scientists in Japan have developed a new organic device that can harvest energy from heat. Unlike other thermoelectric generators, this one works at room temperature without a heat gradient.
Thermoelectric devices are designed to tap into a simple law of physics: heat energy moves from hotter regions to colder ones. In these devices, electrons move from the warmer surface to the cooler one, which produces an electric current. In theory, thermoelectric generators, materials and paints could produce electricity from small temperature differences in engines, power plants, even body heat.
Usually, the bigger the temperature gradient, the better the thermoelectric generator, but now scientists from Kyushu University in Japan have found a way to harness the relatively low energy available from room temperature, without a gradient at all.
Instead, the new device works on a principle called charge separation. Heat from the ambient air causes negative electrons and positive electron “holes” in the material to separate and move in different directions, generating a current.
The materials in question are organic compounds, which can easily transfer electrons between each other. Different types of these compounds are stacked in thin layers like stairs, and the heat gives the electrons or holes enough energy to jump up to the next “step.”
After much trial and error of different compound combinations, the team settled on a device with a 180-nanometer layer of copper phthhalocyanine, 320 nm of copper hexadecafluoro phthalocyanine, 20 nm of fullerene, and 20 nm of bathocuproine.
The end result boasted an open-circuit voltage of 384 millivolts, a short-circuit current density of 1.1 μA/cm2, and a maximum output of 94 nW/cm2. That’s a tiny amount of electricity, of course, but considering it’s coming from room temperature, it could make for simpler generators.
“We would like to continue working on this new device and see if we can optimize it further with different materials,” said Professor Chihaya Adachi, lead author of the study. “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 research was published in the journal Nature Communications.
Source: Kyushu University
