Conventionally designed thermoelectric generators, where one side of the device is hot and the other side is cool to form a temperature gradient, convert heat into electricity. Despite the energy conservation promise of such systems, high production costs, reliance on hazardous materials and the need for relatively high temperatures limit their use. To better exploit such technology, researchers in Japan developed an organic thermoelectric generator that taps the relatively low energy available from room temperature, without a gradient at all.

Different materials tested to identify those that function well as charge transfer interfaces and easily transfer electrons between each other. Copper phthalocyanine (CuPc) and copper hexadecafluoro phthalocyanine (F16CuPc) were identified as suitable compounds for this application. Fullerenes and bathocuproine were also incorporated to further enhance charge transfer.

The device was then structured with a 180 nm layer of CuPc, 320 nm of F₁₆CuPc, 20 nm of fullerene and 20 nm of bathocuproine. The resulting thermoelectric generator demonstrated an open-circuit voltage of 384 mV, a short-circuit current density of 1.1 μA/cm² and a maximum output of 94 nW/cm². As reported in Nature Communications, these results were achieved at room temperature without the use of a temperature gradient.

The researchers from Kyushu University, GCE Institute Inc. and the Institute of Systems, Information Technologies and Nanotechnologies next plan to boost current density by increasing the device’s area.