Holst Centre and Flex-o-Fab take the first step towards "lighting by the mile"

Researchers from the EU-funded Flex-o-Fab project have successfully fabricated working OLED devices on a flexible barrier layer produced in a roll-to-roll (R2R) process. Produced on a PET plastic film, this breakthrough is a significant first step towards taking flexible OLEDs 'from lab to fab' and hence to commercial production. It draws on technical developments achieved within both Flex-o-Fab and Holst Centre's joint research program into high-performance flexible barriers for organic electronics.

OLEDs - or organic light-emitting diodes - hold the promise of flexible, thin, lightweight and power-efficient lighting applications including wearables. They also have the potential to be manufactured in high-volume R2R processes, allowing "lighting by the mile" and greatly reducing productions costs.

However, the materials from which these exciting devices are made are very susceptible to environmental factors and need to be protected from air and moisture. For flexible devices, the conventional approach of producing OLEDs on glass isn't suitable. Holst Centre and its eco-system partners have been at the forefront of developing a flexible, thin-film barrier layer for use with plastic foils, and were the first to produce a high-performance barrier foil in a R2R set-up.

Now, by performing in-situ planarization of the film immediately before depositing the barrier, Holst Centre researchers have been able to deliver R2R barriers that perform similar to barriers produced in sheet-to-sheet (S2S) processes, thereby enabling potential cost savings in volume production. "We have successfully produced over 2.5 kilometers of R2R barrier film based on a single inorganic layer with water vapor transmission rates (WVTR) lower than 10-5 g/m2 per day on commercial-grade PET foil," said Sandeep Unnikrishnan, Roll-to-Roll Barrier project leader at Holst Centre.

The Holst Centre-led Flex-o-Fab project has used that foil to create working OLED devices. To do this, researchers temporarily laminated the barrier foil to a glass substrate before depositing the OLED and then debonding the finished devices. All the OLED devices produced using this roll-to-sheet (R2S) process worked, delivering performance comparable with devices fabricated on S2S barrier foils and with rigid OLEDs on glass.

Conventional equipment was used throughout the process. The devices were produced on a PET film from DuPont Teijin Films, using a debonding adhesive from Henkel for the R2S lamination. Different processing steps were carried out at different partner locations - TNO/Holst Centre (Netherlands), Philips GmbH (Germany) and the

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