A Presentation on Organic Light Emitting Diode By

A Presentation on Organic Light Emitting Diode By Mohammad Tabish Hussain Instrumentation and Control Haldia Institute of Technology 15/IC/32

Introduction • OLED is a solid state light emitting device made from thin films of organic molecules. • It uses the principle of electroluminescence. • It is an emerging technology of displays. • These diodes are about 100 to 500 nanometers thick and 200 times smaller than human hair. • To understand its working let us discuss a little about LED…

Light Emitting Diode • LED is a p-n junction diode. • It emits light in forward bias. • In forward bias, the electron and holes move across the junction and combine. • According to quantum theory when electron comes down from higher energy level to lower level then the energy is emited in the form of light or photon. • The photon energy is equal to energy gap between these to energy levels.

Architecture of OLED • OLED has many thin layers of organic material. • It comprises of two or three organic layers like conducting layer, emissive layer and other layers such as substrate, anode and cathode layers. • When Direct Current is applied, charge carriers from the anode and cathode are injected into organic layers and light is emitted.

• Substrate Layer: This layer is a thin sheet of glass with a transparent conductive layer. It supports OLED structure. • Anode Layer: This layer is an active layer and removes electrons. When current flows through this device, electrons are replaced by electron holes. • Conductive Layer: Also known as hole transport layer as it transport hole from anode layer. This layer is made up of organic plastic. The conductive polymer used in OLED are polyaniline, polyethylene-dioxythiophene.

• Emissive layer: This layer transports electrons from anode layers, and it is made of organic plastic molecules that are different from the conducting layers. In this two polymers are used for emitting such as polyfluorene, poly para phenylene which normally emits green and blue lights. • Cathode Layer: Cathode layer is responsible for injection of electrons when current flows through the device. It could be transparent or opaque depending on the type of OLED.

Working Principle • A voltage is applied across the anode and cathode. • The current flows from cathode to anode through organic layer. • Electron flows to emissive layer from the cathode • Electrons are removed from conductive layer leaving holes

• Holes jump into emissive layer. • Electrons and holes are combined and light is emitted.

Some special types of OLED • Transparent OLED: This OLED consists of transparent substrate, anode and cathode. Lights get emitted bidirectionally. These are useful for heads-up display and transparent projector screens. • Foldable OLED: These OLEDs are made up of flexible metallic foil or plastic substrate. It is light weight and has ultra-thin stature. • Phosphorescent OLED: This OLED works on the principle of electroluminescence used to convert 100 % of the electrical energy into light. They reduce heat generation; operate at very low voltage and have a long operating life time.

Advantages • • • OLED is thinner, lighter and more flexible. It do not requires back light like LCDs. Faster response time. Large field of view about 170 degree. Brighter then other displays. Higher resolution with <5 micrometer pixel size.

Disadvantages • • OLEDs are expensive. Lifespan is less. Balancing of color is not easy. Can be damaged by water.

Conclusion • As OLED technology will mature it will be able to improve certain limitation of current displays. • Organic Light Emitting Diode is evolving as the next generation display.

Referances • www. elprocus. com • Google images

Thank You…