is a LIGHT EMITTING DIODE (LED) in which the Electroluminescent layer is a film of Compounds that are Organic and release light energy when electricity is passed through them. The layer of the Semiconducting materials is situated between two electrodes. OLED belong to either one of two families: Those based on Polymers and those based on small molecules.
Their usage is spread over a wide area of devices and gadgets eg.Television screens, Computer Monitors, Mobile phones,PDA's ,watches and for advertising to mention but a few. The need for the technology especially in lighting is brought about by the fact that some of the traditional sources for lighting e.g. Incandescent lamps, light bulbs, consume about 45-50 % of all the lighting energy and yet produce only about 14% of light which is measured in Lumens. About 90% of the energy goes to the production of heat which is really inefficient. Fluorescent lamps are three to four times more energy efficient, but still, a sizable fraction of the used energy is wasted. Therefore a more efficient lighting method is required. This is where OLED comes into play.
OLEDs are energy converting devices, in that they convert electric power to Light energy based on the process of electroluminescence. Whenever a voltage is applied on to the electrodes, charges move in the device under theinfluence of the electric field. Holes are moved from the anode and Electrons from the cathode.The Recombination of the two charges lead to the formation of a photon which is light energy. The frequency given because of the energy gap is given by(E=hv) Researchers had their eyes on OLEDs during the 1960s because of the Potentially high quantum efficiency of luminescence and the ability to generate a wide variety ofcolors. Unfortunately, due to high operating voltagesof about 1000V it became clear that they were not going to be practical. Not for long though, because in 1987, Dr. Ching Tang and Mr.Van Slyke from Eastman Kodak developed a heterostructure double layered device containing active "small molecules" that combined a low operating voltage of less than 10Volts with good brightnessof greater than 1000 cd/m2 and a respectable luminous efficiency of 1.5lm/W, research once again gained the momentum. In 1990, electroluminescence from polymers was achieved by Burroughes.From then on, OLED research has gained acceleration and as far as device efficiency levels are concerned it has surpassed incandescent lighting.
The advantages of OLEDs include:
- They have a high efficiency in terms of power usage and large area sources.
- They produce a great deal of brightness and the angle of view is wide.
- They are usually thin Flat and FlexibleLow voltage and fast switching technology.
- They allow for form freedom and tunable emissions.
- They are used in flexible displays.
- Water can damage the organic materials of the displays.
- Outdoor performance is poor because the Metallic cathodeusually acts as a mirror leading to poor readability in bright litareas.
- OLED displays can be damaged by overexposure to Ultraviolet Light.
- One of the most discouraging aspect of OLEDs is theirlifespan which can around 14,000 hours to half the original brightness when used for flat-panel displays.
Research is on going to on ways of extending the life spans of the OLEDs and also on lowering down the cost of production. Currently there is a steady market for the technology and the trend looks encouraging for the next foreseeable future.