The Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology (FEP) has developed OLEDs on graphene, a material with high mechanical stability which is expected to increase the reliability of flexible electronics.
Fraunhofer FEP will demonstrate the OLED technology at the Plastic Electronics 2015 conference which takes place 6-8 October in Dresden, Germany.
Until now, transparent electrode materials for OLEDs have mainly consisted of indium tin oxide (ITO); however, the shrinking abundance of indium is expected to create economic challenges for the industry in the future. Therefore, scientists have been exploring the possibility of using alternative materials.
One promising candidate is graphene, and its successful integration into OLEDs by Fraunhofer FEP has come as a result of the project GLADIATOR (Graphene Layers: Production, Characterisation and Integration) funded by the European Commission. The project will run until April 2017 and aims to produce cost-effective, high quality graphene with a large area, which can then be used for numerous electrode applications.
‘Graphene is a very interesting material with many possibilities,’ said Beatrice Beyer, project coordinator. ‘Because of its opto-electrical properties and its excellent mechanical stability, we expect that the reliability of flexible electronics will be improved many times over.’
Graphene is a rediscovered modification of carbon with two-dimensional structure, which has gained popularity since its successful isolation in 2004. Such so-called ‘monolayer’ graphene is synthesised on a metal catalyst via a chemical vapour deposition (CVD) process and transferred by a further process step to a target substrate, such as thin glass or plastic film. Here, it is very important that no defects are added which might reduce the quality of the electrode.
In order to compete with the reference material indium tin oxide, the transparency and conductivity of graphene must be very high.
Therefore, not only the process of electrode manufacturing is being optimised, but also different ways of doping graphene to improve its properties are being examined. At the same time, the developed process steps must be easily scalable for later industrial use.
For the GLADIATOR project, scientists have been examining the integration of graphene and comparing it to indium tin oxide. So far, defect-free OLEDs on transparent graphene electrodes have been realised on small areas.
During the next one and a half years, Fraunhofer FEP aims to successfully illuminate large area OLEDs.
By the time the project concludes in 2017, several types of OLED will have been produced using graphene electrodes: a white OLED with an area of about 42cm2 to demonstrate the high conductivity, and a fully-flexible, transparent OLED with an area of 3 cm2 to confirm the mechanical reliability.
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