Presented By
Paulomi Deekonda

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ABSTRACT
Organic Light-emitting Diodes (OLEDs) are just like a movie projector screen in theearlier times with a thin sheet hanged on the wall in which the screen was light, paperthinand could be rolled into portable tube. The materials used in OLEDs need not becrystalline that is composed of a precisely repeating pattern of planes of atoms, so theyare easier to make. They are applied in thin layers for slimmer profiles and differentmaterials for different colours that can be patterned on a given substrate for making highresolution images. In the coming years, large screen televisions or computer monitorscould roll up for storage. A soldier might unfurl a sheet of plastic showing a real timesituation map. Smaller displays could be wrapped around a person’s forearms orincorporated into clothing. The OLED panels could curl around an architectural columnor lay almost wall paper like against a wall or ceiling.
ORGANIC LIGHT - EMITTING DIODES
1. INTRODUCTION:
An organic light emitting diode (OLED) is simply a light emitting diode (LED) whoseemissive electro luminescent layer is composed of a film of organic compounds. The layersare made up of small organic molecules or macro polymers that conduct electricity. Theyhave conductivity levels ranging from insulators to conductors, so OLEDs are considered asorganic semiconductors. The layer of organic semiconductor material is formed between twoelectrodes, where at least one of the layers is transparent.
2. SURFACE CONSTRUCTION OF OLED ILLUMINATION:
It consists of an emissive layer, a conductive layer, a substrate, and both anode and cathodeterminals. The emissive layer, where light is made by the emission of radiation whosefrequency is in the visible region is made up of organic plastic molecules that transportelectrons from the cathode and the polymer used is polyfluorene. The conductive layer ismade up of organic plastic molecules that transport holes from the anode and the conductingpolymer used is polyaniline. The substrate that supports OLED is made up of flexible plastic,inexpensive glass or metal foil. Anode, that removes electrons when a current flows throughthe device, is generally made up of Indium tin oxide and it is transparent and cathode thatinjects electrons when a current flows through the device is made up of metals likealuminium and calcium, which may or may not be transparent depending on the type ofOLED.4OLED structure
3. LIGHT EMISSION PRINCIPLE :
OLEDs emit light in a similar manner to LEDs, through a process called electrophosphorescence.An electrical current flows from the cathode to the anode through theorganic layers. When a voltage is applied to OLED, the holes and the electrons are generatedfrom each of the two electrodes, which have a positive and negative electric chargerespectively. When they recombine in the emissive layer, organic materials make theemissive layer to turn into a high energy state termed “excitation”. The light is emitted whenthe layer returns to its original stability. The molecular structure of organic materials haslimitless combinations, each of which varies in its colour and durability. Within theselimitless combinations, identifying organic materials that provide high efficiency and longlife will determine its practical application.A semi-conducting material such as silicon has an energy gap between its lower, filledelectrons state called as valence band and its upper, unfilled electrons state called asconduction band. As electrons drop to the lower state and occupy holes, photons of visiblelight are emitted. The colour of the light depends on the type of organic molecule in theemissive layer and the intensity or brightness of the light depends on the amount of electricalcurrent applied.
4. CREATION OF COLOUR
OLED has more control over colour expression because it only expresses pure colours whenelectric current stimulates the relevant pixels. The primary colour matrix is arranged in red,green and blue pixels which are mounted directly to a printed circuited board. Eachindividual OLED element is housed in a special micro cavity structure designed to greatlyreduce ambient light interference that also improves overall colour contrast. The thickness ofthe organic layer is adjusted to produce the strongest light to give a colour picture. Further,the colours are refined with a filter and purified without using a polarizer to give outstandingcolour purity.