Organic chemistry on the telly
It's the ultimate in hi-tech TV, and it's arrived just in time for Christmas. On 1 December, Sony launches the XEL-1 - the world's first OLED (organic light-emitting diode) television.
The new XEL-1: the skinniest telly around
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The launch may be more about prestige than profits. 'I want this world's first OLED TV to be the symbol of the revival of Sony's technological prowess,' said Sony president Ryoji Chubachi. A company that has traditionally traded on its high-tech image, Sony has lost its lead in portable music players to Apple's iPod, and more recently has fallen behind Nintendo in the computer games market.
While the XEL-1 is the first OLED device to hit this end of the market, OLED display technology is already widely available in small-screen products such as mobile phones, and in Sony's own Walkman-branded portable music player range.
Small OLED screens can be controlled relatively easily using a passive matrix approach, in which rows of anodes are positioned perpendicular to rows of cathodes. Each point where the electrodes cross forms a pixel, with the full image formed by firing each pixel in turn. 'OLEDs have a real edge in small screens because they have an extremely low component count, so can be made very cheaply,' said John de Mello of Imperial College, London, UK. However, this system requires a high drive current to brightly illuminate each pixel, which becomes inefficient in larger screens.
Instead, the larger screen of the XEL-1 uses an active matrix, where each pixel is controlled by individual transistors that can all be fired at once, making the technology much more complex.
But the pay-off is a higher quality picture than can be achieved with LCDs. 'OLED displays are thinner, and brighter, so they give better colours and blacks, and they have a wider viewing angle,' Alexandra Gay of Cambridge Display Technology, UK, told Chemistry World.
'Sony clearly thinks there will be people prepared to pay a premium for the form-factor and the picture quality,' said de Mello, whose own research into OLEDs has spawned a spin-out company called Molecular Vision. 'But OLED TVs are up against stiff competition,' he added. 'LCDs have been getting better and better, and cheaper and cheaper.'
Throw away your television
OLED polymers have been around for at least fifteen years - but in terms of market potential, have been held back by the materials' short lifetime. 'The lifetime of the material is mostly down to the purity of the polymer,' said Klaus Meerholz, University of Cologne, Germany. 'The impurities are at levels so low they can't be detected, so its very hard to say what they are - but if you make the purity better, the lifetime gets better.'
Most OLED device development is carried out in Asia, particularly South Korea and Japan. But Europe is active in researching these essential materials, said Meerholz, who collaborates with Merck OLED Materials GmbH.
'It has taken a long time to piece together, but now we have very efficient materials that last for a long period of time,' agreed de Mello.
While Sony is the first electronics giant to launch an OLED television, all the major LCD-producing companies are involved in OLED research to a greater or lesser extent, and several, including Samsung and LG Philips LCD, have produced prototypes. 'In the short term, not all companies are necessarily intending to release a device - but it's just too risky not to have some involvement in OLEDs,' said de Mello.
James Mitchell Crow
How OLED TV works
OLED displays consist of one or more thin layers of semiconducting materials such as polyfluorines or iridium-based organometallics. These are sandwiched between two electrodes, one of which (usually an indium-tin oxide cathode) is transparent.
The organic molecules in the semiconducting layer incorporate many conjugated double bonds, which form a delocalised electron cloud. Applying a voltage removes electrons from this delocalised system at the anode (forming 'holes'), while introducing extra electrons at the cathode. Following the electric field, the electrons and holes meet to form an exciton - a tightly bound electron-hole pair - which decays to give a photon. So where LCD screens require a backlight, which makes the screens wider and more complex, in OLEDs the organic layer itself generates the light.
OLEDs also hold great promise for lighting, since they are an extremely efficient way of converting electricity into light. However, white OLEDs currently produce an unpleasantly harsh light, so current research is focused on developing softer colours.