Researchers Dan Zhao and Simone Fabiano from at the Laboratory of Organic Electronics, Linköping University, have created a thermoelectric organic transistor. A temperature rise of a single degree is sufficient to cause a detectable current modulation in the transistor.
According to the researchers the heat-driven transistor opens the possibility of many new applications such as detecting small temperature differences, and using functional medical dressings in which the healing process can be monitored.
It is also proposed that it would also be possible to produce circuits controlled by the heat present in infrared light, for use in heat cameras and other applications. The high sensitivity to heat, 100 times greater than traditional thermoelectric materials, means that a single connector from the heat-sensitive electrolyte, which acts as sensor, to the transistor circuit is sufficient. One sensor can be combined with one transistor to create a "smart pixel".
A matrix of smart pixels can then be used, for example, instead of the sensors that are currently used to detect infrared radiation in heat cameras. With more developments, the new technology can potentially enable a new heat camera in your mobile phone at a low cost, since the materials required are neither expensive, rare nor hazardous.
The heat-driven transistor builds on research that led to a supercapacitor being produced a year ago, charged by the sun's rays. In the capacitor, heat is converted to electricity, which can then be stored in the capacitor until it is needed.
The researchers at the Laboratory of Organic Electronics had searched among conducting polymers and produced a liquid electrolyte with a 100 times greater ability to convert a temperature gradient to electric voltage than the electrolytes previously used. The liquid electrolyte consists of ions and conducting polymer molecules. The positively charged ions are small and move rapidly, while the negatively charged polymer molecules are large and heavy. When one side is heated, the small ions move rapidly towards the cold side and a voltage difference arises.
Dan Zhao, principal research engineer, and Simone Fabiano, senior lecturer, have shown, after many hours in the laboratory, that it is fully possible to build electronic circuits that are controlled by a heat signal.
Since 2014 the research has been financed by the Knut and Alice Wallenberg Foundation as part of the "Tail of the sun" project.
Professor Xavier Crispin of the Laboratory of Organic Electronics, Linköping University, said, "We are the first in the world to present a logic circuit, in this case a transistor, that is controlled by a heat signal instead of an electrical signal." Xavier added, "When we had shown that the capacitor worked, we started to look for other applications of the new electrolyte."
Article | OPEN
Ionic thermoelectric gating organic transistors
Dan Zhao | Simone Fabiano | Magnus Berggren | Xavier Crispin
Nature Communications 8 | Article number: 14214 (2017) | doi:10.1038/ncomms14214
Received: 01 August 2016 | Accepted: 08 December 2016 | Published online: 31 January 2017
Abstract
Temperature is one of the most important environmental stimuli to record and amplify. While traditional thermoelectric materials are attractive for temperature/heat flow sensing applications, their sensitivity is limited by their low Seebeck coefficient (∼100 μV K−1). Here we take advantage of the large ionic thermoelectric Seebeck coefficient found in polymer electrolytes (∼10,000 μV K−1) to introduce the concept of ionic thermoelectric gating a low-voltage organic transistor. The temperature sensing amplification of such ionic thermoelectric-gated devices is thousands of times superior to that of a single thermoelectric leg in traditional thermopiles. This suggests that ionic thermoelectric sensors offer a way to go beyond the limitations of traditional thermopiles and pyroelectric detectors. These findings pave the way for new infrared-gated electronic circuits with potential applications in photonics, thermography and electronic-skins.