The transistor that's driven by heat

Researchers from Linköping University have created a thermoelectric organic transistor — apparently the first in the world to be controlled by a heat signal rather than an electrical signal. Their work has been published in the journal Nature Communications.

The transistor (pictured) builds on a study that last year led to the development of a supercapacitor being charged by the Sun’s rays, in which the Sun’s heat is converted to electricity and then stored in the capacitor until required. This study relied on a liquid electrolyte — consisting of small, quick, positively charged ions and large, heavy, negatively charged conductive polymers — located between two metal electrodes.

When one end of the electrolytes was heated and the other one cooled down, the small ions rushed towards the cold side while the heavy polymer chains stayed where they were. The ions stuck to the metal electrodes and the charge that arose was stored in carbon nanotubes next to the metal electrodes, available for discharge whenever electricity was needed.

“When we had shown that the capacitor worked, we started to look for other applications of the new electrolyte,” said Professor Xavier Crispin.

After many hours in the laboratory, Professor Crispin and his colleagues showed that it was possible to build a logic circuit — in this case, a transistor — that is controlled by a heat signal. Furthermore, its sensitivity to heat — 100 times greater than traditional thermoelectric materials — means that a temperature rise of a single degree is sufficient to cause a detectable current modulation in the transistor.

The heat-driven transistor could potentially be used for applications such as detecting small temperature differences and in functional medical dressings in which the healing process can be monitored. It is also possible to produce circuits controlled by the heat present in infrared light, for use in heat cameras and other applications.

Image credit: Thor Balkhed.