Roll-coating organic LED is first step to cheaper fabrication

Light-emitting-diode (LED) displays are typically made by the batch using vacuum deposition chambers, but researchers at Pacific Northwest Laboratory (Richland, WA) recently demonstrated a fast and continuous method for depositing a film of the active layer of small-molecule organic LEDs onto a flexible plastic substrate.

This proof-of-principle experiment used roll-coating, a method developed for plastics, paper, and other roll goods. The light-emitting small-molecule organic dopant was added to a tris-8-(hydroxyquinoline)-aluminum host and then sprayed onto the substrate as a liquid. The process allows the manufacturer to switch liquid sources without stopping the coater.

Click here to enlarge image

The demonstration showed that doped films can be produced by premixing the host and dopant instead of carefully controlling co-evaporation rates. The resulting film showed quantum efficiencies similar to vapor-deposited films. Researcher Paul Burrows reports that spectroscopy shows no residual emission from the host, which is "important for color purity and as a demonstration that we got enough of the dopant in."

If the encapsulate and electrical contact layers can also be deposited by this method, then entire large-area displays could be made very quickly and relatively inexpensively.

Yvonne Carts-Powell is a freelance writer living in Belmont, MA; e-mail:

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