Optimized Printing Process for Organic Electronics
Organic electronics is considered a very promising market for the future. Products such as touchscreens, sensors and solar cells are already being manufactured from electrically conductive plastic. Flexible monitors and luminous wallpaper based on organic LEDs are already in development. These products are manufactured by printing conductive, semi-conductive or insulating layers in a specific sequence on a carrier film. As part of an international cooperation project, physicists at the Technical University of Munich have now been able to observe the creation of extremely thin polymer electrodes during the printing process and improve the electrical properties of the printed films.
For their investigation, the researchers used high-intensity x-ray radiation that permits a very high time resolution. The x-rays are directed onto the freshly printed plastic layer, where they are scattered. The arrangement and orientation of the molecules after curing of the printed films can be determined from the scattering patterns. The researchers noted that even small changes to the physical-chemical process conditions had a significant effect on the structure and properties of the layer. The addition of solvents with a high boiling point, for instance, results in better crystallization of the conductive molecules. The distance between the molecules decreases and conductivity increases.
In this way, the stability and conductivity can be increased to the point where the material can even be used as a transparent electrical contact. Previously, indium-tin oxide layers frequently served as contacts to the flexible conductive layers. The oxide is relatively brittle, however, and limits the flexibility of the cells. Furthermore, indium is available only in very limited quantities. The results of the research studies could mean that it will be possible to use the same process to produce all layers. Work is now focused on developing the materials for industrial-scale use.