An organic light-emitting diode (OLED) is a light-emitting diode (LED) made of semiconducting organic polymers. These devices promise to be much cheaper to fabricate than inorganic LEDs. Varying amounts of OLEDs can be deposited in arrays on a screen using simple "printing" methods to create a graphical colour display, for use as television screens, computer displays, portable system screens, and in advertising and information board applications. OLED panels may also be used as lighting devices. OLEDs are available as distributed sources while the inorganic LEDs are point sources of light. Prior to standardization, OLED technology was also referred to as OEL or Organic Electro-Luminescence.

One of the great benefits of an OLED display over the traditional LCD displays found in computer displays is that OLED displays don't require a backlight to function. This means that they draw far less power and they can be used with small portable devices which have mostly been using monochrome low-resolution displays to conserve power. This will also mean that they will be able to last for long periods of time with the same amount of battery charge.

The world's first digital camera with an OLED display was the Kodak LS633 model revealed at the Photo Marketing Association (PMA) trade show in March 2003.

There are two main directions in OLED.

The first technology was developed by Eastman-Kodak and is usually referred to as "small-molecule" OLED. The production of Small-molecule displays requires vacuum deposition which makes the production process expensive and not so flexible.

A second technology, developed by Cambridge Display Technologies or CDT, is called LEP or Light-Emitting Polymer.The light-emitting polymer material consists of chains of molecules. Although this technology lags the Small-Molecule development by several years, it is more promising because of an easier production technique. No vacuum is required, and the OEL materials can be applied on the substrate by a technique derived from commercial ink-jet printing. This means that LEP displays can be made in a very flexible and cheap way.

OLEDs work on the principle of Electroluminescence. The key to the operation of an OLED is an organic dye. This dye has exciton states, which consist of an excited electron and a hole (empty state) it can fall into. When the electron and hole combine, a photon is emitted. The tricky part is the creation of the proper excitons. It can be done by shining light on the dye, which creates fluorescence. But the goal is to have a device that emits its own light.

To create the excitons, a thin film of the dye is used, and a current is passed through it in a special way. Excited electrons are injected into one side from a metal cathode, while holes are injected in the other from an anode (think of the anode as sucking electrons out of the dye). These electrons and holes move into the dye and meet to form excitons. Then when the excitons decay (the electron falls into the hole), they often give off the light we are looking for.

Derivatives of PPV, poly(p-phenylene vinylene), are commonly used as the polymer dyes in OLEDs. Indium tin oxide is a common anode, while aluminum is a common cathode. Other materials are added in between the cathode/anode and the dye layer to enhance the efficiency. You may find more materials for this technology.

The radically different manufacturing process of OLEDs lends itself to many advantages over traditional flat panel displays. Since OLEDs can be printed onto a substrate using traditional ink-jet technology they have a significantly lower cost than LCDs or plasma displays. A more scalable manufacturing process enables the possibility of much larger displays. Unlike LCDs which employ a back-light and are incapable of showing true black, an off OLED element produces no light allowing for infinite contrast ratios. The range of colors and brightness possible with OLEDs is greater than that of LCDs or plasma displays.

Without the need of a backlight, OLEDs use less than half the power of LCD displays and are well-suited to mobile applications such as cell phones and digital cameras.

The fact that OLEDs can be printed onto flexible substrates opens the door to new applications such as roll-up displays or displays embedded in clothing.

The biggest technical problem left to overcome now is lifetime. Red and green OLED elements already have life-times of well over 20,000 hours but blue OLED life-times lag significantly behind at 1,000 hours.

The lifetime problems are not so significant in small molecule OLEDs, particularly as a result of doping of OLEDs has led to much better device performance both electrically and optically. Universal Display for example have produced a blue OLED that has a lifetime of 10,000 hours. There are still a number of problems to overcome though, and one of these is intrusion of water into displays which damages and destroys the organics, as well as outcoupling, which can result in the loss of much of the light in waveguided modes within the substrates.

In October 2004 Cambridge Display Technology announced a blue OLED with a lifetime of 30,000 hours.

Development of the technology is also hampered by IP issues since even the basics of OLED technology is heavily patented by Kodak and other firms, requiring outside research teams to acquire a license.

• Howard, Webster E. (Feb. 2004). Better Displays with Organic Films. Scientific American, p. 76.
• Shinar, Joseph (Ed.) (2004). Organic Light-Emitting Devices: A Survey. NY: Springer-Verlag. ISBN 0-387-95343-4.

• Flexible electronics

• CDT achieves blue lifetime of 70,000 hours
• Samsung announces 21" OLED 01/05
• Samsung announces 'largest ever' organic LED display (ZDNet uk, 21 May 2004)
• On line Forum to Discuss about Organic device such as OLED
• Overview of OLED Display Technology

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