Organic displays show bright future

Organic electroluminescent diode elements based on complexes of rare earth and other metals, have now reached the point where they can be incorporated into the next generation of displays. Production problems have largely been overcome, all colours are available, including CRT blue, lifetimes are plenty long enough for use in mobile phones and similar devices, and electrical efficiencies are ten times those of LCDs. Research groups around the world are engaged in a race to bring the next generation of flat colour screens to market. Professor Kathirgamanathan, and has his team at Elam-T, now based at the London BIC in Enfield, are, however convinced that they are winning it. Lifetimes of more than 5,000 hours with no change in luminance are now being regularly achieved. This is partly thanks to the purchase of a new £1 million Japanese machine that allows test displays to be moved from chamber to chamber through the production process, without exposing them to air or moisture at any point. All the colours of the rainbow are now available, including CRT red and blue. Light intensities are mostly up to 4,000 cd/m2, although one substance achieves 15,000 cd/m2, brighter than many fluorescent light tubes. Elam-T now has a set of materials suitable for passive matrix displays, which includes the 15,000 cd/m2, and materials for active matrix displays, with lower operating voltages but consequently lower brightnesses. Materials are available for vacuum or solution, ink jet printed, processing. Looking to markets, 5,000 hours life is sufficient for the mobile phone market, and Professor Kathir expects to see Elam-T's materials in commercial products in about 18 months. An important factor is the ability to take existing production equipment and adapt it to working with the new technology. Large, flat screens are thought not likely to be achievable using passive matrix technology, which rules out most of the other organic light emitting diode technologies currently being developed. LCDs are continuing to be developed, and presently achieve lives of 50,000 hours, but are likely to continue to suffer from relatively low electrical efficiencies, because of light absorbed by the different dyes and polarisers. They are also not nearly as robust as users would like. If either the screen or lamp is broken, replacement is usually so expensive that the phone or laptop has to be thrown away. It can therefore be safely assumed that light emitting diode technology is going to replace LCDs before too long, and the latter technology is therefore likely to be one with the dinosaurs, even in large screens, before five years are out. Professor Kathirgamanathan Pointers * All colours are available including CRT red, green and blue as well as yellow * Lifetimes are now in excess of 5,000 hours with no change in luminosity * Brightnesses are up to 15,000 cd/m2