Using its patented process, FEP was able to modify the emission of an OLED through the existing encapsulation layer to achieve full-colour OLED without using colour filters or shadow masks, creating a fixed image. To create red, green, and blue pixels, an organic layer of the OLED itself is ablated by a thermal electron beam process. This patterning causes a change to the thickness of the layer stack, which makes the emission of different colours possible. This is the first major step towards the development of full-colour displays without the use of restrictive colour filters in the process, claims Fraunhofer FEP.
“With our electron-beam process it is possible to thermally structure even these sensitive organic materials without damaging the underlying layer”, explained Elisabeth Bodenstein, developer in the Fraunhofer FEP project team.
The results were obtained by simulating and initially estimating the HTL (hole-transport layer) thicknesses that are produced by the electron beam. The researchers actually achieved the decoupling of red, green, and blue emissions from the white OLED. Following proof of concept at Fraunhofer FEP, these colours were demonstrated on the first test substrates, exhibiting comparable OLED performance.
In addition to using this new process for OLEDs, electron beam processing can also be used for other applications in organic electronics and inorganic layers. Moreover, the electron-beam patterning process is very adaptable and can also be employed in the areas of photovoltaics, MEMS, and thin-film technology.
Next, the researchers aim to use this new method for the joint development and fabrication of OLED microdisplays with partners and establish it in the industry through licensing, with further miniaturization, process optimization and eventually micro-patterning integration into existing processes. The scientists are also planning an enhanced simulation of OLEDs. The OLED colour spectrum will be broadened by suitably modifying the materials and layer thicknesses.
This new technology is the result of a project funded by the Fraunhofer-Gesellschaft. First samples of coloured OLEDs will also be presented at the Fraunhofer FEP booth no. 50 and in poster session III during the International Meeting on Information Display – IMID 2018 in Busan, South Korea, August 29-31, 2018.
Fraunhofer FEP – www.fep.fraunhofer.de