Building on existing technologies and innovating new processes, the project’s partners achieved indium-free electrodes and brighter OLEDs. Overall, the project has strengthened Europe’s leading position in the lighting industry by taking flexible OLEDs a giant step closer to commercial reality.
More robust than their rigid, glass-based counterparts, flexible OLEDs open up a whole new field of lighting systems. Thin, lightweight, bendable and transparent, they can be embedded into all kinds of everyday objects – imagination is the only limit to their potential applications. And with the completion of the European funded Flex-o-Fab project in 2015, such applications are now much closer to commercial reality.
Coordinated by Holst Centre, an independent open-innovation R&D center, the three-year Flex-o-Fab project aimed at realizing the technologies needed for industrialization of flexible OLEDs. By developing reliable processes for manufacturing OLEDs on plastic foils, Flex-o-Fab has successfully taken flexible OLEDs from lab to fab. To do this, the project used a distributed pilot production line and associated manufacturing chain involving partners and facilities at different locations across Europe.
The project’s goals included reducing costs and enabling higher volume production. One of the main achievements towards these was the migration of key processes from existing sheet-to-sheet (S2S) to roll-to-roll (R2R) production. This was enabled by developing existing technologies and creating new processes. The resulting flexible OLEDs are based on an R2R multilayer barrier technology developed by Holst Centre. Overall, the project has achieved what it set out to do by making a larger scale demonstration of the hybrid process chain to produce flexible OLED lighting panels.
“We contributed significant expertise throughout the process, especially in the areas of barrier and electrode substrate technology”, said Date Moet, project coordinator and research scientist at Holst Centre. “It is very gratifying to see the project realize industrially relevant results. There has been positive feedback from the European Commission, showing they value the progress that has been made in making OLEDs in the hybrid R2R/S2S process in higher numbers.”
Among the key achievements of the project are the creation of an indium-free transparent conductive oxide (TCO) and an increased brightness in the flexible OLED solution.
The new, indium-free electrode for the flexible OLEDs was developed by project partner École Polytechnique Fédérale de Lausanne (EPFL). “Indium, the main component of indium tin oxide (ITO) widely used in electrodes for flexible applications, is rare and expensive, especially for use at industrial scale,” said EPFL team leader Monica Morales-Masis. “Zinc-tin oxide (ZTO), an all earth-abundant TCO, has the same mechanical and chemical stability as ITO, but its relatively poor electrical properties have limited its use. We overcame this drawback by improving the conductivity of the ZTO electrode and choosing the right metal grid to support it. When integrated in flexible OLEDs, our ZTO-metal grid electrode outperformed reference ITO-based OLEDs1. By replacing ITO with indium-free ZTO we significantly reduced cost, making the technology more applicable for volume production.”
Light emission was enhanced by about 30% compared to ITO through a substrate developed by DuPont Teijin Films (DTF), which used plastic with outcoupling features. In an S2S process, a brightness of 10,000 cd/m2 was achieved for a white flexible OLED. This shows just how much progress has been made: changing from rigid glass to a flexible, 0.2-mm-thick light source while maintaining luminance, homogeneity and visual quality. Furthermore, as all the processes are compatible with R2R production, there are no technical barriers to stop Flex-o-Fab’s hybrid R2R/S2S process being up-scaled further to R2R.
The future also looks positive. Various projects are in place to carry on from the success of Flex-o-Fab. For example, OLEDWorks is excited by the substantial market interest shown in flexible OLEDs. “As a key industrial player linked to the project, OLEDWorks will build further on the results obtained and is now exploring the potential use of these processes in further commercialization of flexible OLEDs,” said Eric Meulenkamp, general manager at OLEDWorks GmbH.