The History and Future of OLED

OLEDs have gained much popularity throughout the past year, but what does it stand for, what does it do and what is to come of it?

What is OLED?

Organic Light-Emitting Diode is any light emitting diode (LED) which emissive electroluminescent layer is composed of a film of organic compounds. Usually, it contains a polymer substance that allows an organic compound to be deposited. The compounds are deposited in rows and columns onto a flat carrier by a printing process, resulting in a matrix of pixels that can emit light of different colors.

The system can then be used for television screens, computer displays, portable system screens, or simply be used as a light bulb.Typical OLEDs emit less light per area than inorganic solid-state LEDs that are designed as a point-light source.

History of OLED

Bernanose and co-workers produced the first electroluminescence in the early 1950s by applying high-voltage alternating current field to crystalline thin films of acridine orange and quinacrine. In 1960, researchers at Dow Chemical developed AC-driven electroluminescent cells using doped anthracene.

In 1963, Weiss et al. First reported high conductivity in iodine-doped oxidized polypyrrole with a conductivity of 1 S/cm. As of 1974, the discovery was called “lost” and a melanin-based bistable switch with a high conductivity “ON” state. The material emitted a flash of light when switched.

In a 1977 paper, Shirakawa et al. Reported high conductivity in similarly oxidized and iodine-doped polyacetylene. The group subsequently won the 2000 Nobel Prize in Chemistry for the discovery and development of conductive organic polymers.

Future of OLED

• POLED – Patternable OLED. Uses a light or heat activated electroactive layer. A latent material is included in the layer so when it is activated, it becomes highly efficient as a hole injection layer, preparing LED and arbitrary patterns.
• FOLED – Flexible OLED. Any flexible OLED display. Thin enough to be rolled up like a poster and carried anywhere, even embedded in clothing.
• TOLED – Transparent OLED. A proprietary transparent contact to create displays that can be made to be top only emitting, bottom-only emitting, or both top and bottom emitting (transparent). TOLEDs can greatly improve contrast, making it easier to view displays in bright sunlight.
• SOLED – Stacked OLED. A novel pixel architecture that is based on stacking RGB subpixels on top of one another instead of next to one another—common in CRT and LCD. This improves display resolutions up to threefold and enhances full-color quality.
• IOLED – Inverted OLED. A bottom cathode that can be connected to the drain end of n-channel TFT especially for the low cost a-Si TFT backbone useful in manufacturing of AMOLED display, contrast to a conventional OLED which anode is placed on the substrate.
• WOLED – White OLED. White OLED has the potential to reach 150 lm/W. High powered, environmentally friendly, bright and uniform.
• PHOLED – Phosphorescent OLED. Phosphorescent OLED uses the principle of electrophosphorescence to convert up to 100% of the electrical energy in an OLED into light.

Advantages

• Can be printed onto any suitable substrate using an inkjet printer.
• Will cost significantly lower than LCD or plasma displays.
• A greater range of colors, brightness and viewing angle than LCDs, because OLED directly emits light. Colors appear correct and unshifted, even as the viewing angle approaches 90 degrees from normal. LCDs use a backlight and cannot show true black, while an “off” OLED element produces no light and consumes no power.
• Energy is wasted in LCDs because they require polarizers that filter out half of the light emitted by the backlight. Color filters in color LCDs filter out two-thirds of the light.
• OLEDs also have a faster response time than standard LCD screens. LCDs currently have a response time of 8-12 milliseconds whereas OLEDs can have less than 0.01ms.

Disadvantages

• Limited lifetime of organic materials.
• Blue OLED has a lifetime of 5,000 hours – lower than typical LCD, LED or PDP, currently around 60,000 hours. Nevertheless, Green PLEDs have been tested for 198,000 and Blue PLEDs 62,000 hours.
• Water in displays can damage or destroy the organic materials. Improved sealing is a must, and may limit longevity of the more flexible displays.
• Commercial developments have been limited by patents held by Eastman Kodak and other firms, requiring companies to acquire licenses.

Written: Jan 26, 2008
Tags: displays, foled, oled, television

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