Flexible OLED light sources on transparent electrodes developed within TREASORES. These OLEDs were made by Fraunhofer FEP using a roll-to-roll process. Credit: Fraunhofer FEP
In >3yrs of work, European scientists have finally made future lighting technology ready to market. They developed flexible lighting foils that can be produced roll-to-roll. These devices pave the path towards cheaper solar cells and LED lighting panels. Project TREASORES was lead by Empa scientist Frank Nüesch and combined knowhow from 9 companies and 6 research institutes in 5 european countries.
In Nov 2012, the TREASORES project (Transparent Electrodes for Large Area Large Scale Production of Organic Optoelectronic Devices) started with the aim of developing technologies to dramatically reduce the production costs of organic electronic devices. It has produced 7 patent applications, a dozen peer-reviewed publications and provided inputs to international standards organisations. Most importantly, the project has developed and scaled up production processes for several new transparent electrode and barrier materials for use in the next generation of flexible optoelectronics.
3 of these electrodes-on-flexible substrates that use either carbon nanotubes, metal fibres or thin silver are either already being produced commercially, or expected to be so as of this year. The new electrodes have been tested with several types of optoelectronic devices using rolls of over 100 meters in length, and found to be especially suitable for next-generation light sources and solar cells. The roll of OLED light sources with the project logo was made using roll-to-roll techniques on a thin silver electrode. Such processing techniques promise to make light sources and solar cells much cheaper in future, but require flexible and transparent electrodes and water impermeable barriers – also developed by the TREASORES project. The electrodes from the project are technically at least as good as those currently used (made from indium tin oxide, ITO) but will be cheaper to manufacture and do not rely on the import of indium. Due to the new electrodes, OLED light source was very homogeneous over a large area, achieving an efficiency of 25 lumens per watt – as good as the much slower sheet to sheet production process for equivalent devices. New test methods were developed by the National Physical Laboratory in the UK to ensure electrodes would still work after being repeatedly bent – a test that may become a standard in the field.
A further outcome of the project has been the development, testing and production scale-up of new approaches to transparent barrier foils (plastic layers that prevent oxygen and water vapour from reaching the sensitive organic electronic devices). High performance low-cost barriers were produced and it is expected that the Swiss company Amcor Flexibles Kreuzlingen will adopt this technology after further development. Such high performance barriers are essential for long device lifetimes – as confirmed by a life cycle analysis (LCA). By combining the production of barriers with electrodes (instead of using 2 separate plastic substrates), the project has shown that production costs can be further reduced and devices made thinner and more flexible.
The main challenge the project had to face was to make the barrier and electrode foils extremely flat, smooth and clean. Optoelectronic devices have active layers of only a few hundred nanometres and even small surface irregularities or invisibly tiny dust particles can ruin the device yield or lead to uneven illumination and short lifetimes.
https://www.empa.ch/web/s604/treasores-oled-results
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