Organic LED, the commonly called OLED is a solid state semiconductor light emitting diode having a thickness of 100 to 500 nanometers. It is also called as Organic Electro Luminescent Device (OELD) These devices are currently used in small screen displays such as mobile screen, digital camera etc. The OLED display is much thinner than LCD and consumes less power. Research in the field of OLED is progressing and many manufacturers are trying to make OLED displays in TV, computer monitor etc
Organic LED is formed of aggregates of Amorphous and Crystalline molecules without definite arrangement. The OLED has many thin layers of organic material which emit light through the process of Electrophosphoresence. The organic material uses substances that can emit red, green blue and white lights. When a potential is applied to the cathode and anode, OLED creates light which appears as the display.
Organic LED is a solid state device like the LED but composed of several layers .OLED may have two or three layers of organic material along with other layers. The different layers of OLED are
1. Substrate layer-It supports OLED and is made up of transparent plastic or glass film
2. Anode layer – It is a transparent layer that removes electrons. Indium tin oxide is commonly used as the anode material.
3. Organic layer – Layer formed of organic polymers
4. Conductive layer – Transports holes from anode. Made up of organic plastic. Polymer light-emitting diodes (PLED), also light-emitting polymers (LEP), are used in electroluminescent conductive polymer. Typical polymers used in PLED displays include derivatives of poly(p-phenylene vinylene) and polyfluorene.
5. Emissive layer – Transports electrons from the cathode layer. It is made up of organic plastic
6. Cathode layer – Injects electrons. It may be transparent or not. Metals such as Aluminium
and Calcium are often used in the cathode
How it emit light?
Organic LEDs are brighter devices than LED or LCD. They can give clear video pictures and pictures that can be viewed from any angle. The process of light emission in OLED includes different stages
1. When a potential difference is applied between the anode and cathode of OLED, current flows through the organic layer of OLED.
2. During the flow of current, cathode layer emits electrons to the emissive layer.
3. Anode then gives electrons from the conductive layer creating holes.
4. These electrons combine with the holes in junction between the emissive and conductive layers.
5. When the electrons combine with holes, the energy of electrons is emitted as photons. Color of the photons depends on the type of the organic material in the emissive layer.
Forms of Organic LEDs
There are different types of OLED based on the construction.
1. Transparent OLED – They have all transparent components like anode, cathode and substrate.
2. Top emitting OLED – Substrate layer is reflective or opaque
3. White OLED – Emit white light. These can be made into large sheets to make fluorescent lamps
4. Foldable OLED – Substrate layer is flexible and foldable. Used in cell phones to avoid damage.
5. Active matrix OLED – They have all layers but the anode layer has a transistor array that determines the pixel of the display.
6. Passive OLED – Has strips of cathode and anode. External circuit determines the pixel in these devices.
Conventional TV, LCD TV and OLED TV