Unlike ITO electrodes, carbon nanotubes are not brittle and do not crack as easily when submitted to bending tests. Furthermore, carbon nanotube deposition processes can be accomplished at room temperature, which means that organic layers are not damaged during fabrication.

In their research, the scientists are investigating the possibility of using carbon nanotubes to construct organic semiconducting devices such as OLEDs on practically any surface. Given that the transparent electrode is the last layer deposited, the working substrate does not need to be transparent. To explore the idea in more detail, a top emission OLED, as shown in the figure above, has been fabricated and characterized.

The carbon nanotube starting material is in powder form. In order to make uniformly thin and transparent films, the first step is to disperse the powder in an aqueous solution. The solution is then filtered through a membrane filter to form a highly uniform film. Varying the amount of nanotube solution filtered will result in different transparencies and conductivities. Depending on the type of filter used, it’s possible to use an elastomeric stamp to pick up this film from the filter and deposit it on the desired surface. This process is called "micro-contact printing" and it is compatible with roll-to-roll manufacturing techniques, which would help to lower production costs.

The group’s preliminary results were obtained on a glass substrate for simplicity. The next step is to fabricate such devices on a textile substrate coated with some sort of planarization layer. Many challenges remain, but the researchers believe that they are now one step closer to making wearable affordable OLED displays a reality.

Further details can be found in the journal Nanotechnology.