From OLEDs to LECs

Ultra-thin and electricity-saving organic light diodes, OLEDs, have been introduced commercially in mobile phones, cameras and super-thin TVs.

An OLED consists of a light-generating layer of plastic placed between two electrodes, one of which must be transparent. Today’s OLEDs have two drawbacks - they are relatively expensive to produce and the transparent electrode consists of the metal alloy indium tin oxide.

The latter presents a problem because indium is both rare and expensive and is complicated to recycle.

Now, researchers at Linköping and Umeå universities, working with American colleagues, are presenting an alternative to OLEDs, an organic light-emitting electrochemical cell (LEC) that is inexpensive to produce and the transparent electrode is made of the carbon material graphene.

The invention, which could pave the way for glowing wallpaper made entirely of plastic, for example, is published in the scientific journal ACS Nano by scientists at Linköping University and Umeå University, in Sweden, and Rutgers, the state university of New Jersey.

“This is a major step forward in the development of organic lighting components, from both a technological and an environmental perspective. Organic electronics components promise to become extremely common in exciting new applications in the future, but this can create major recycling problems.

“By using graphene instead of conventional metal electrodes, components of the future will be much easier to recycle and thereby environmentally attractive,” says one of the scientists, Nathaniel Robinson from Linköping University.

Since all the LEC’s parts can be produced from liquid solutions, it also will be possible to make LECs in a roll-to-roll process on, for example, a printing press.

“This paves the way for inexpensive production of entirely plastic-based lighting and display components in the form of large flexible sheets. This kind of illumination or display can be rolled up or can be applied as wallpaper or on ceilings,” says another of the scientists, Ludvig Edman from Umeå University.

Graphene consists of a single layer of carbon atoms and has many attractive properties as an electronic material. It has high conductivity, is virtually transparent and can be produced as a solution in the form of graphene oxide.