Organic Light Emitting Diode

Organic Light Emitting Diode is a scalable nano level emerging technology in Flat Panel Displays and as a White Light Source with efficient features. This paper focuses on OLED structure, principle aspects, fabrication methodology and different techniques to replace current white light sources like Incandescent bulbs, Fluorescent tubes, and even display techniques like Liquid Crystal Displays, Plasma technologies. OLEDs can be fabricated using Polymers or by small molecules. OLED matrix displays offer high contrast, wide viewing angle and a broad temperature range at low power consumption. These are Cheaper, Sharper, Thinner, and Flexible. OLEDs have a potential of being white-light sources that are

• Bright, power-efficient and long lived, by emitting pleasing white light

• Ultra-thin, light weight, rugged, and conformable

• Inexpensive, portable

OLEDs are energy conversion devices (electricity-to-light) based on Electroluminescence. Electro-luminescence is light emission from a solid through which an electric current is passed. OLEDs are more energy-efficient than incandescent lamps. The luminous efficiency of light bulbs is about 13 - 20 lm/W but the latest experimental green emitting OLEDs already have luminous efficiency of 76 lm/W, though at low luminance. The development is on track for OLEDs to effectively compete even with fluorescent lamps, which have the luminous efficiency of 50 - 100 lm/W. One big advantage of OLEDs is the ability to tune the light emission to any desired color, and any shade of color or intensity, including white. Achieving the high Color Rendition Index (CRI) near 100 (the ability to simulate the most pleasing white color, sunlight), is already within the reach of OLEDs. Another advantage of OLEDs is that they are current-driven devices, where brightness can be varied over a very wide dynamic range and they operate uniformly, without flicker.

CRT is still continuing as top technology in displays to produce economically best displays. The first best look of it is its Cost. But the main problems with it are its bulkiness, Difficulties in Extending to Large area displays as per construction. Even though Liquid Crystal Displays have solved one of problem i.e. size, but it is not economical. So in this present scenario the need for a new technology with both these features combined leaded to invention of OLED.OLED which is a thin, flexible, Bright LED with self luminance which can be used as a display device. The main drawback of LCD display is its Less viewing angle and highly temperature depending which moves us towards a new technology. Thus OLED promises for faithful replacement of current technology with added flavors like Less Power Consumption and Self Luminance .Both Active matrix TFT’s and Passive matrix Technologies are used for display and addressing purposes for high speed display of moving pictures and faster response. Already some of the companies released Cell Phones and PDA’s with bright OLED technology for color full displays.

Organic Light Emitting Diodes (OLEDs) are thin-film multi-layer devices consisting of a substrate foil, film or plate (rigid or flexible), an electrode layer, layers of active materials, a counter electrode layer, and a protective barrier layer At least one of the electrodes must be transparent to light.

The OLEDs operate in the following manner: Voltage bias is applied on the electrodes, the voltages are low, from 2.5 to ~ 20 V, but the active layers are so thin (~10Å to 100nm) that the electric fields in the active layers are very high, of the order of 105 – 107 V/cm. These high, near-breakdown electric fields support injection of charges across the electrode / active layers interfaces. Holes are injected from the anode, which is typically transparent, and electrons are injected from the cathode. The injected charges migrate against each other in the opposite directions, and eventually meet and recombine. Recombination energy is released and the molecule or a polymer segment in which the recombination occurs, reaches an exited state. Excitons may migrate from molecule to molecule. Eventually, some molecules or a polymer segments release the energy as photons or heat. It is desirable that all the excess excitation energy is released as photons (light).

The materials that are used to bring the charges to the recombination sites are usually (but not always) poor photon emitters (most of the excitation energy is released as heat). Therefore, suitable dopants are added, which first transfer the energy from the original excitons, and release the energy more efficiently as photons. In OLEDs, approximately 25% of the excisions are in the singlet 

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  • Raj Janorkar

    Organic Light Emitting Diode

    2 years ago