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Organic Light Emitting Diodes (OLED)
Post: #1


Scientific research in the area of semiconducting organic materials as the active substance in light emitting diodes (LEDs) has increased immensely during the last four decades. Organic semiconductors was first reported in the 60Confused and then the materials where only considered to be merely a scientific curiosity. (They are named organic because they consist primarily of carbon, hydrogen and oxygen.). However when it was recognized in the eighties that many of them are photoconductive under visible light, industrial interests were attracted. Many major electronic companies, such as Philips and Pioneer, are today investing a considerable amount of money in the science of organic electronic and optoelectronic devices. The major reason for the big attention to these devices is that they possibly could be much more efficient than todays components when it comes to power consumption and produced light. Common light emitters today, Light Emitting Diodes (LEDs) and ordinary light bulbs consume more power than organic diodes do. And the strive to decrease power consumption is always something of matter. Other reasons for the industrial attention are i.e. that eventually organic full color displays will replace todays liquid crystal displays (LCDs) used in laptop computers and may even one day replace our ordinary CRT-screens.

Organic light-emitting devices (OLEDs) operate on the principle of converting electrical energy into light, a phenomenon known as electroluminescence. They exploit the properties of certain organic materials which emit light when an electric current passes through them. In its simplest form, an OLED consists of a layer of this luminescent material sandwiched between two electrodes. When an electric current is passed between the electrodes, through the organic layer, light is emitted with a color that depends on the particular material used. In order to observe the light emitted by an OLED, at least one of the electrodes must be transparent.

When OLEDs are used as pixels in flat panel displays they have some advantages over backlit active-matrix LCD displays - greater viewing angle, lighter weight, and quicker response. Since only the part of the display that is actually lit up consumes power, the most efficient OLEDs available today use less power.
Based on these advantages, OLEDs have been proposed for a wide range of display applications including magnified microdisplays, wearable, head-mounted computers, digital cameras, personal digital assistants, smart pagers, virtual reality games, and mobile phones as well as medical, automotive, and other industrial applications.


Electronically, OLED is similar to old-fashioned LEDs -- put a low voltage across them and they glow. But that's as far as the similarity goes: instead of being made out of semiconducting metals, OLEDs are made from polymers, plastics or other carbon-containing compounds. These can be made very cheaply and turned into devices without all the expensive palaver that goes with semiconductor fabrication.

Light-emitting diodes, based upon semiconductors such as Gallium Arsenide, Gallium Phosphide, and, most recently, Gallium Nitride, have been around since the late '50s. They are mostly used as indicator lamps, although they were used in calculators before liquid crystals, and are used in large advertising signs, where they are valued for very long life and high brightness. Such crystalline LEDs are not inexpensive, and it is very difficult to integrate them into small high-resolution displays.
Post: #2
can yu send me the full report for the topic -Organic light emitting diodes
Post: #3
i want a full report and an abstract will also do.
Post: #4
(26-07-2009 06:05 PM)electronix Wrote:  i want a full report and an abstract will also do.
Post: #5
A N organic light-emitting diode (OLED) is a special type of light-emitting diode (LED). An OLED is composed of an undoped organic layer that is sandwiched between two
electrodes. Electrons and holes are injected from either side of the electrode which drift due to the applied electric field. excitons are formed when electrons and holes meet at the bulk or the interface. These excitons will decay to produce light emission. based on the materials used for OLEDs, they can be divided into twoclasses: small-molecular OLEDs and polymer light-emitting diodes (PLEDs). Generally, an OLED refers to small-molecular OLED.

a) Device structure:
A small-molecular OLED consists of one organic layer or multiple organic layers between two electrodes. A one organic layer device is called a single layer device. The
organic material must serve all the three main functions: electron transport, hole transport and emission. multiple organic layers in the OLED structure result in high efficiency because there is no surplus uncombined electrons.
The three layers in a typical OLED are:
1)employs an electron transport layer (ETL),
2) a hole transport layer
3)Emissive layer

b) Electrodes
one electrode should be transparent to allow the emission of light from the
device. indium-tin-oxide (ITO) is commonly used for this purpose. for anodes are Al, Ma, Ca, etc are used.

The typically used n-type materials for ETL are Alq3, PBD,
etc. And the generally used p-type materials for HTL are NPB
and TPD, etc.

polymers are usually deposited by dissolving an organic solvent followed by spin-coating,
drop-casting, ink-jet printing or roll-to-roll web coating. This is because they have high molecular weights and cannot be fabricated using conventional methods.

1)Solid-State Lighting:
the power efficiency of an OLED has already achieved 30-60
lm/W in the laboratory Therefore, OLED will be a good
candidate for the new generation of the solid-state lighting.

2)Flat-Panel Displays
OLED displays offer higher contrast, truer colors, higher
brightness, wider viewing angles, better temperature tolerance,
and faster response times than LC displays, which make it have
the potential to be the next-generation of the display device.
OLED displays do not have to be back-lit. Thusthey have the potential
thinner, lighter and more flexible than conventional LC
displays. It can be also used in large screens and flexible.

Full report download:

Post: #6
see for more information on Organic Light Emitting Diodes (OLED)

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