Large area printing
How to cut the cost of producing polymer semiconductors in large volumes? Holst Centre and its partners are addressing this question by investigating large area printing techniques. The results could be useful for applications including lighting, signage, organic photovoltaics (OPVs), thin film batteries and sensors.
The program focuses mainly on processes for future volume production of polymer-based organic light emitting diodes (PLEDs). For this, very thin, patterned layers of (semi-)conducting polymers need to be created with an extremely uniform thickness. Printing these layers is considerably cheaper than other production techniques such as vacuum deposition.
Today’s printing applications, such as a typical desktop printer, typically cram around 50,000 pixels into a single square centimeter. By contrast, PLEDs for lighting and signage applications require printed features measured in square centimeters or even square meters.
Maintaining a uniform thickness over such large print areas is a big challenge. Our early investigations showed that the four most promising technologies for further development are:
- Inkjet printing
- Flexographic printing
- Gravure printing
- Slot-die coating
Each one currently has its own strengths and weaknesses. The first three can print any shape required, but don’t yet offer the necessary layer thinness or uniformity. By contrast, slot-die coating can produce extremely uniform thin layers but only in certain formats. The challenge now is to ‘close the gap’.
Development is already well advanced. To help make the move into production, the program brings together people from throughout the value chain and from both sides of the academia-industry border. These include mathematicians, physicists, chemists and design and process engineers. The wide range of the program stretches from theory to demonstrator, and includes both batch and roll-to-roll production.