Printing OLED displays: has their time finally come? Asks IDTechEx

February 25, 2019 //By Dr Khasha Ghaffarzadeh
Printing OLED displays: has their time finally come? Asks IDTechEx
Solution processed light emitting organic materials were demonstrated in 1989 with a tiny 0.1 EQE (external quantum efficiency). Since then there has been tremendous progress on material synthesis/production as well as on display processing. However, thus far, commercialization has remained elusive, but a page may be about to turn.

This could have important consequences for the large area display markets, especially if printing can enable a significant reduction in the production cost.

Today, there are two main approaches to OLED display production. Both use evaporated organics. In one, the emissive layers are evaporated through a fine metal mask (FMM) to achieve patterned side-by-side R, G, and B emitters. This approach works well for small up to medium sized displays. Indeed, today, it fully dominates the market for such products.

The technology however has proven difficult to scale up to large areas. The FMM is often made very thin to minimise shadowing effects during the evaporation. The downside of this thinness is that wide area masks become flimsy, easily sagging or warping under their own weight. This distorts the mask pattern. The FMM also, by definition, blocks and thus wastes 2/3 of the material. The blocked materials further add weight to the mask film, further aggravating the situation.

Numerous approaches have been proposed to overcome these shortcomings, for example using a scanner over the substrate. None have, however, fully resolved the issues. Therefore, FMM has failed to transition to large area displays. The other approach is based upon white OLED (WOLED). Here, the organic layers are not patterned. Instead, they are blanket deposited. This way multiple OLED stacks are formed on top of one another to achieve white colour emission. In this approach, it is often common to have two blue layers to divide the drive voltage across two stacks whilst maintaining the brightness levels.


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