The Holst Centre in Eindhoven, the Netherlands, has worked with a US ultra-thin ceramics supplier, ENrG Inc., to create a ceramic-based large area flexible OLED. The substrate is a 20-40 µm thick Thin E-Strate ceramic surface that is claimed to have a life of more than 10 years without the formation of blackspots, but is also claimed to be easier to handle than other materials because of the ability to withstand temperatures up to 1000ºC. There are options to make the substrate semi-transparent and the Centre said that this helps to improve outcoupling and thus higher device efficacy.
The protection the OLED receives, and hence its potential durability, is typically quantified through its water vapour transmission rate (WVTR). In tests, the Thin E-Strate-based OLED demonstrated a WVTR below 8.5 x 10-7 g/m²/day. In addition, while most flexible OLEDs require a multi-layer barrier on both sides, the Holst Centre-ENrG device achieved these values with the ceramic layer at the bottom and a Holst Centre thin film top encapsulation, directly deposited by plasma enhanced chemical vapour deposition (PECVD) and printing of a few layers.
“A WVTR of less than 10-6 g/m²/day is widely accepted as a minimum requirement for commercial devices. At this level, it takes over 10 years for deterioration due to moisture to lead to visible black spots. But such a rating is difficult to achieve, and many other flexible OLEDs with single-layer barriers have around 10-5 g/m2/day or higher (equivalent to a 1 year lifetime or less). Beating the 10-6 g/m²/day target with such a simple structure shows the excellent protection of Thin E-Strate and Holst Centre’s direct thin film encapsulation stack on top. This approach could help further reduce complexity for flexible OLED production,” said Hylke Akkerman, Senior Scientist at Holst Centre.
