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Introduction

This page is to help in the understanding of how OLEDs work. And what OLEDs are.

I think I know enough (having attempted to write two thesis sections on them!) to give a basic explanation about them, but if not I can at least provide links to where there is a good source of information about how they work, what they are, their application, and news about recent developments with them.

It should also be noted that the following explanation is aimed at people with some chemistry/physics knowledge.

Organic Light Emitting Diodes

These are devices made up of organic materials (usually polymeric in nature) layered in such a way as to enable the emission of light, or organic electroluminescence, upon the passage of current through the material. Electrons are injected into the LUMO (lowest unoccupied molecular orbital) of the organic material and holes are injected into the HOMO (highest occupied m.o.). This process forms something called radical anions and radical cations. These are charges which, when an electric field is applied to the device, move together, sort of hopping from molecule to molecule within the polymeric material. Upon combination they form a local ‘excited state’, and it is on relaxation from this ‘excited state’ that emission can be seen.

Below is a basic schematic of an OLED, as published in the journal Nature (full citation: ELECTROLUMINESCENCE IN CONJUGATED POLYMERS; Nature, 1999, 397, 121)

As can be seen (hopefully the resolution isn’t too poor) the device is made up of several layers, with the polymeric p-phenylenevinylene being the organic layer responsible for the luminescence.

Below is another image (www.howstuffworks.com) which shows an example OLED schematic, with a second polymer layer which ultimately allows for better transport of electrons and holes within the devices, and as such more light can be emitted.

Why are OLED Displays better than LCD Displays?

First of all are the advantageous costs. Processing/production of the organic based devices is estimated to be much, much cheaper than that of the inorganic devices used in displays today.

Secondly, due the nature of the materials being investigated - namely the polymeric layers which are the emissive components) - the devices can be made to be very flexible. This opens the technology up to a host of as-yet-unknown uses, as well as the production of roll-up screens of the style used with over-head projectors today, and electronic paper (e-paper).

Thirdly is the increase in quality of the display. Resolutions will be higher, with a much wider perceived viewing angle.

Good sources on the subject:

http://komar.cs.stthomas.edu/qm425/01s/Tollefsrud2.htm

http://en.wikipedia.org/wiki/OLED

http://electronics.howstuffworks.com/oled.htm

For a good demonstration and more about the technology:

http://www.oled-display.net/how-works-the-oled-technology

It should be noted this is an incomplete work, since they are a fascinating and quite complicated area of science which is only just being fully understood (by me especially!). To that end, please don’t consider this a full brief on the workings or the developments, as they are continuing to happen, quite literally, on a daily basis.

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