US researchers claim to have developed robust and reusable organic light-emitting diodes (OLEDs) comprising layers held together purely by van der Waals forces. The forces are weak enough to allow the layers to be peeled apart and reused.

OLEDs are generally constructed by evaporating a metal layer onto an organic layer. The problem with this technique is that the metal can eventually diffuse into the organic layer and disrupt the chemical bonds.

Researchers from Bell Laboratories at Lucent Technologies, US, and from the University of Illinois at Urbana-Champaign, have used a new technique called soft contact lamination to create OLEDs which don’t suffer from such disruption. They claim that OLEDs made in this way perform better than those made using standard processing techniques.

The soft contact lamination process is done at room temperature and pressure and involves bringing together a transparent elastomeric layer coated with a thin metal film and a layer composed of an electrode embedded in a film of electroluminescent material. As the layers approach each other, van der Waals forces pull them together.

The researchers claim that the layers stay together even when the OLED is turned upside down. However, the layers can also be peeled apart and reused. According to Tae-Woo Lee, who led the team, this enables researchers to alter the layers to improve the OLED’s performance. ‘For example, the top electrode can be modified at a molecular scale by attaching single small molecules to the metal,’ Lee notes. This can help to prevent the metal layer migrating into the organic layer.

The research team is still working on improving the OLEDs. ‘The soft contact lamination approach is also one of the most promising methods for developing highly efficient and stable organic devices for commercialisation,’ says Lee. He imagines that it would only take three to five years to take the new OLEDs to market. According to Lee, the research team is currently developing several different types of soft contact laminated devices which operate at low voltage to improve ‘luminous efficiency and operational stability’. ED

(Proc. Natl. Acad. Sci. USA, 2004, 101, 429)