Scientists in Japan have developed a new organic device that can harvest energy from heat. Unlike other thermoelectric generators, this device works at room temperature without any thermal gradient.
Thermoelectric devices are designed to take advantage of a simple law of physics: thermal energy moves from areas of higher temperature to areas of lower temperature. In these devices, electrons move from a hotter surface to a cooler surface, generating an electric current. In theory, thermoelectric generators, materials, and paints could produce electricity from tiny temperature differences in engines, power plants, and even body heat.
Typically, the larger the temperature gradient, the better the performance of a thermoelectric generator, but scientists at Kyushu University in Japan have found a way to harness the relatively low energy available from room temperature without any gradient at all.
Instead, the new device works on a principle called charge separation: heat from the surrounding air causes negative electrons and positive electron “holes” in the material to separate and move in different directions, generating an electric current.
The materials in question are organic compounds that can easily move electrons between each other: Different types of compounds are stacked in thin layers, like stairs, and heat is used to give electrons or holes enough energy to jump to the next “step”.
After much trial and error with different compound combinations, the team settled on a device made of a 180-nanometer layer of copper phthalocyanine, 320 nanometers of copper hexadecafluorophthalocyanine, 20 nanometers of fullerene, and 20 nanometers of bathocuproine.
The final result boasted an open circuit voltage of 384 millivolts, a short circuit current density of 1.1 μA/cm2, and a maximum power output of 94 nW/cm2. Of course, this is a tiny amount of electricity, but considering that it occurs at room temperature, it could be a simpler generator.
“We would like to continue developing this new device and see if we can further optimize it with different materials,” said Professor Chihaya Adachi, lead author of the study. “If we increase the area of the device, we could probably achieve a higher current density, which is unusual even for organic materials. This shows that organic materials have amazing potential.”
The study was published in the journal Nature Communications.
Source: Kyushu University
