Graphene is clear candidate as transparent electrode for OLEDs
The OLEDs on show are an interim result from the project GLADIATOR funded by the European Commission.
Until now transparent electrode materials for OLEDs have mainly consisted of indium tin oxide (ITO), which is expected to become economically challenging for the industry due to the shrinking abundance of indium. Scientists are looking for alternatives with one promising candidate being graphene, whose application fields are being closely investigated as part of project GLADIATOR.
Project GLADIATOR has reached its midterm and has already achieved some successes. The aim of the project is the cost-effective production of high quality graphene in large areas, which can then be used for numerous electrode applications. The usability of such applications will be demonstrated at the Fraunhofer FEP by integrating the graphene produced in OLEDs.
Using graphene as an electrode, the researchers at the Fraunhofer FEP hope to create flexible devices with higher stability. Beatrice Beyer, project coordinator, said: “Graphene is a very interesting material with many possibilities. 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.”
The ‘monolayer’ graphene is synthesized 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 and it is important that no defects are added which might reduce the quality of the electrode. In order to compete with the reference material ITO, the transparency and conductivity of graphene must be high. The researchers are not only optimizing the process of electrode manufacturing but also examining different ways of doping graphene to improve its properties.
At the same time, the developed process steps must be easily scalable for later industrial use. The varied challenges are being faced by the project consortium consisting of sixteen partners from six EU member states and Switzerland.
The Fraunhofer FEP is coordinating the GLADIATOR project and acts as an end-user of the graphene electrode. The scientists are examining the integration of graphene and compare it to the reference material ITO. The sophisticated material properties of graphene must be maintained during the integration in organic devices. To this end, several methods for cleaning and structuring the graphene must be modified. In addition, the processes for different target substrates such as glass or flexible foil must be adapted and optimized. The first hurdles have been overcome thanks to a close cooperation between the consortium partners and the first defect-free OLEDs on transparent graphene electrodes have been realized on small areas. The target of the next one and a half years is to successfully illuminate large area OLEDs.
The GLADIATOR project will run until April 2017. By this time several types of OLED will have been made using graphene electrodes: a white OLED with an area of about 42 cm2 to demonstrate the high conductivity, and a fully-flexible, transparent OLED with an area of 3 cm2 to confirm the mechanical reliability.
The OLEDs on graphene will be demonstrated at Plastic Electronics 2015 on booth 1549, which is the joint booth of OES – Organic Electronic Saxony.
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