lsemiconductors are very useful devices for amplification of signals, switching, and energy conversion.

lThis effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determine

lElectroluminescence-is an optical phenomenon and electrical phenomenon in which a material emits light in response to the passag

lDiscovered in 1907 by the British experimenter H. J. Round of Marconi Labs, using a crystal of silicon carbide and a cat's

lDow Chemical researchers patented a method of preparing electroluminescent cells using high voltage (500

lElectroluminescence from polymer films was first observed by Roger Partridge at the National Physical Laboratory in the Unite

Schematic of a Bilayer OLED

1. Cathode (−), 2. Emissive Layer, 3. Emission of radiation, 4. Conductive Layer, 5. Anode (+)

Working principle

lVoltage is applied across the OLED such that the anode is positive w.r.t the cathode.

lA current of electrons flows through the device from cathode to anode, as electrons are injected into the LUMO of the organic

lElectrostatic forces bring the electrons and the holes towards each other and they recombine forming an exciton, a bound stat

lIn organic semiconductors holes are generally more mobile than electrons, results in a relaxation of the energy levels of the

lThe frequency of this radiation depends on the band gap i.e (energy gap where no e- exixt) of the material.

lLight weight & flexible plastic substrates

lBy fabricating possiblity of flexible organic light-emitting diodes being fabricated or other new applications such as roll

lBetter power efficiency

lOLED element does not produce light or consume power.

lAnd response time is also higher than standard LCD screens.

Disadvantages

lCurrent costs

lOLED manufacture currently its extremely expensive.

lLifespan

lThe biggest technical problem for OLEDs was the limited lifetime of the organic materials.

lWater damage

lWater can damage the organic materials so sealing processes are important for practical manufacturing.

Manufacturers and commercial uses

lOLED technology is used in commercial applications such as displays for mobile phones and portable digital media players, car

lOLEDs have been used in most Motorola and Samsung colour cell phones, as well as some HTC, LG and Sony Ericsson models.

lNokia has also introduced some OLED products including the N85 and the N86 8MP, both of which feature an AMOLED display.

lThe Google and HTC Nexus One smartphone includes an AMOLED screen, as does HTC's own Desire and Legend phones.

Magnified image of the AMOLED screen on the Google

Sony XEL-1, the world's first OLED TV

lOn June 25, 2012, Sony and Panasonic announced a joint venture for creating low cost mass production OLED televisions by 2013

lOn December 26, 2011, LG officially announced the "world's largest 55" OLED panel" .

lMitsubishi installed a 6-meter OLED 'sphere' in Tokyo's Science Museum