Organic light emitting devices (Oleds) use carbon-based materials with photo-electric properties similar to the Led lights on your PC: they glow when they pass current. But they are far more versatile. Cambridge Display Technology's (CDT's) light-emitting polymers (Leps) are called 'big molecule' to distinguish them from 'small-molecule' Oleds developed by Kodak (polymers - familiar in the form of plastics - consist of molecules built around long chains of carbon atoms). Kodak has already demonstrated full-colour Oled screens big enough for a sub-notebook. As with Lep screens, the most striking thing is that they can be viewed from a wide angle.

CDT believes its technology has the edge as its screens can be printed while Kodak's requires a more expensive deposition process. A company called Opsys, in conjunction with St Andrews and Oxford Universities, is working on an exotic class of molecule called light-emitting dendrimers that it says combines the best of both technologies. A dendrimer (see picture) consists of a light-emitting core surrounded by charge-carrying branch-like structures called dendrons reaching out to a surface of atomic clusters that repel each other to produce a large, sprung, ball-like molecule. Opsys says the core can consist of the kind of material Kodak uses for its small-molecule screens.

The surrounding molecular structure separates each light-emitting element and provides solubility that enables Lep-style printing of screens. The core can be adjusted for qualities such as colour without affecting the outer structure. But dendrimer technology is less mature than Lep and is likely to take longer to translate into products.

A US company called Universal Display is also working on flexible Oled screens and has produced moulded screens for use in military head-up displays. Similar mouldings could transform dashboards and even cartons into dynamic displays.

In a future issue we'll let you know about another potentially revolutionary carbon-based technology based on nanotubes.

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