New light-emitting tattoos have a variety of applications

Researchers have demonstrated an easy way to transfer ultrathin organic light-emitting diodes (OLEDs) to temporary tattoo paper that can be applied to any kind of surface. The result is a light-emitting tattoo.

The storable tattoos have a wide range of possible uses, from diagnostic electrocardiograms and biomedical monitoring on skin, to showing expiration dates on packaging of produce. 

The proof-of-concept study was conducted by scientists in Italy, England and Austria, and published in the March issue of Advanced Electronic Materials.

The work is of "remarkable importance," the authors write, "as the first demonstration of disposable OLED tattoos with scalable and ultra-cheap fabrication techniques." The devices have a further advantage of being easy to apply and easy to wash off with soap and water.

OLEDs are already used in flat-screen displays for smart phones and other portable devices, where they use an organic semiconductor material that emits light when an electric current is applied. The new work was able to reduce the OLED thickness and make the devices flexible and able to conform to virtually any type of surface.

Using a commercial temporary tattoo paper as a substrate, the researchers fabricated a green-emitting OLED device on top of it.

The device consists of five layers. An ink jet is used to print an electrode pattern on both sides of an electroluminescent polymer layer. An insulating layer goes between the electrodes and the tattoo paper. Spin coating and thermal evaporation are used to fabricate the layers.

The completed device is only 2.3 micrometers thick, which is less than one-400th of a millimeter. The researchers expect to reduce this even further when they are able to optimize the fabrication process of the layers.

To transfer the OLED tattoo to its target, the tattoo paper is moistened on the paper side. This dissolves its water soluble layer, and allows the paper to slide out leaving the OLED tattoo on the selected surface.

The OLED devices now are able to operate only for a few minutes, but the researchers expect that this operation time can be lengthened. "Optimization of the device structure with additional functional layers, adoption of inherently more stable materials, and/or of appropriate encapsulation will improve performance and extend OLED tattoos lifetime." 

The authors conclude by noting that their "results show the potential for implementing an OLED tattoo technology in integrated conformable electronic circuits, potentially also paving the way for a new generation of portable, low cost, and low power displays."