A team of researchers has created an innovative organic thermoelectric device that can generate electricity from the surrounding ambient temperature. While existing thermoelectric devices have various applications, stumbling blocks continue to hinder their optimal use. By leveraging the distinctive characteristics of organic materials, the researchers formed a framework for thermoelectric energy generation at room temperature, eliminating the need for a temperature gradient. Their research results were featured in the journal Nature Communications.
Thermoelectric devices, often referred to as thermoelectric generators, are materials designed to transform heat into electrical energy as long as there is a temperature difference between two sides of the device – where one side is heated and the other is cooler. There has been significant focus on the research and development of these devices due to their potential to capture waste heat from various energy-producing processes.
One prominent example of thermoelectric generators is found in space exploration. Machines like the Mars Curiosity rover and the Voyager probe utilize radioisotope thermoelectric generators. Here, the heat created from radioactive isotopes provides the necessary temperature gradient for the thermoelectric components to operate and power the instruments onboard. However, challenges such as high production costs, the use of toxic materials, low energy efficiency, and the need for elevated temperatures have kept thermoelectric devices from being fully exploited in modern applications.
“Our team was exploring methods to design a thermoelectric device that could harness energy from ambient temperature. Our laboratory specializes in organic compounds, many of which possess unique traits that allow for efficient energy transfer among them,” states Professor Chihaya Adachi, who is the head of the Center for Organic Photonics and Electronics Research (OPERA) at Kyushu University. “A notable illustration of the effectiveness of organic compounds can be seen in OLEDs and organic solar cells.”
The challenge lay in identifying compounds suitable for charge transfer interfaces—those capable of easily transferring electrons to one another. Through testing various materials, the team identified two effective compounds: copper phthalocyanine (CuPc) and copper hexadecafluoro phthalocyanine (F16CuPc).
“To enhance the thermoelectric performance of this new interface, we also integrated fullerenes and BCP,” Adachi continues. “These materials are recognized as excellent enhancers of electron transport. By combining these compounds, we markedly improved the device’s power output. Ultimately, our optimized device consisted of a 180 nm layer of CuPc, 320 nm of F16CuPc, followed by 20 nm of fullerene, and 20 nm of BCP.”
The optimized device produced an open-circuit voltage of 384 mV, a short-circuit current density of 1.1 μA/cm2, and achieved a maximum output of 94 nW/cm2. Impressively, all of these metrics were fulfilled at room temperature without the necessity of a temperature gradient.
“There have been significant advancements in the field of thermoelectric devices, and our newly introduced organic device will certainly contribute to evolving this area,” concludes Adachi. “We aim to continue refining this device by testing additional materials. It’s likely we could achieve a higher current density simply by enlarging the device’s surface area, which is quite atypical even for organic materials. This illustrates the remarkable potential of organic materials.”
