Transparent, Ultra-Sensitive Heat Sensor Shows Promise for Wound Healing, Electronic Skin, and Smart Buildings

A new, ultra-sensitive heat sensor created by researchers at the Laboratory of Organic Electronics is printable, flexible, and transparent. The outcomes hold promise for an array of applications, ranging from electronic skin and wound healing to smart buildings.

The novel ultra-sensitive heat sensor is built on the fact that some materials have thermoelectric properties. In the case of a thermoelectric material, the electrons reach the warm side from the cold side whenever a temperature variation occurs between the two sides, followed by a rise in voltage variation. However, in this latest project, the scientists have created a thermoelectric material that utilizes ions—rather than electrons—as charge carriers, thereby resulting in an impact that is many times larger.

A thermoelectric material that utilizes electrons can develop as much as 100 µV/K (microvolt per Kelvin), which has to be evaluated against 10 mV/K from the novel material. Therefore, the signal is 100-fold stronger, and even a slight variation in temperature releases a powerful signal.

Nature Communications

The findings of the study, performed by researchers at the Laboratory of Organic Electronics at Linköping University, Stuttgart Media University, the University of Kentucky, and the Chalmers University of Technology, have been reported in Nature Communications.

The innovative material was discovered by Dan Zhao, a research fellow at Linköping University and also one of three main authors of the article. The material is an electrolyte containing a gel of a number of ionic polymers. Certain components are p-type polymers, in which the current is carried by positively charged ions. Polymers like these are known well from earlier studies. Conversely, Zhao has also identified an n-type polymer gel that is highly conductive and in which the current is carried by negatively charged ions. Until now, very few of these materials have been available in the market.

First printed thermoelectric module in the world

Now, using the earlier results obtained from the study focused on electrolytes for printed electronics, the team has come up with the world’s first printed thermoelectric module that uses ions as charge carriers, rather than electrons.

The new thermoelectric module contains linked p- and n-legs, in which the number of leg connections ascertains the extent of the strength of a signal that is generated. Screen printing was used by the research team to develop a highly sensitive heat sensor, predicated on the complementary and different polymers. The heat sensor is capable of changing a slight difference in temperature to a robust signal—a module integrated with 36 connected legs provides 0.333 V for a temperature variation of 1 K.

The material is transparent, soft and flexible and can be used in a highly sensitive product that can be printed and in this way used on large surfaces. Applications are found within wound healing, where a bandage that shows the progress of the healing process is used, and for electronic skin.

Dan Zhao, Study Principal Author and Research Fellow, Linköping University

Temperature exchange in smart buildings represents another potential application.

Apart from Dan Zhao, the article in Nature Communications includes two more principal authors—Xavier Crispin, professor in organic electronics, and Simone Fabiano, head of research within organic nanoelectronics. All three authors work at the Laboratory of Organic Electronics, Campus Norrköping.

The study has been funded by, among other sources, the Tail of the Sun project, the Knut and Alice Wallenberg Foundation, the Swedish Foundation for Strategic Research, the Swedish Research Council and Vinnova.