Organic light-emitting diode
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Demonstration of a flexible OLED device
A green emitting OLED device
An organic light emitting diode (OLED) is a light-emitting diode (LED) in which the emissive electroluminescent layer is a film of organic compounds which emit light in response to an electric current. This layer of organic semiconductor material issituated between two electrodes. Generally, at least one of these electrodes is transparent.
OLEDs are used in television set screens, computer monitors, small, portable system screens such as mobile phones and PDAs,watches, advertising, information, and indication. OLEDs are also used in large-area light-emitting elements for general illumination. Due to their low thermal conductivity, they typicallyemit less light per area than inorganic LEDs.
An OLED display works without a backlight. Thus, it can display deep black levels and can be thinner and lighter than liquid crystal displays. In low ambient light conditions such as dark rooms, an OLED screen can achieve a higher contrast ratio than an LCD—whether the LCD uses either cold cathode fluorescent lamps or the more recently developedLED backlight.
There are two main families of OLEDs: those based on small molecules and those employing polymers. Adding mobile ions to an OLED creates a Light-emitting Electrochemical Cell or LEC, which has a slightly different mode of operation.
OLED displays can use either passive-matrix (PMOLED) or active-matrix addressing schemes. Active-matrix OLEDs (AMOLED) require a thin-filmtransistor backplane to switch each individual pixel on or off, but allow for higher resolution and larger display sizes.
2 Working principle
3 Material technologies
3.1 Small molecules
3.2 Polymer light-emitting diodes
3.3 Phosphorescent materials
4 Device Architectures
4.2 Patterning technologies4.3 Backplane technologies
7 Manufacturers and commercial uses
7.1 Samsung applications
7.2 Sony applications
7.3 LG applications
8 See also
10 Further reading
11 External links
The first observations of electroluminescence in organic materials were in the early1950s by A. Bernanose and co-workers at the Nancy-Université, France. They applied high-voltage alternating current (AC) fields in air to materials such as acridine orange, either deposited on or dissolved in cellulose or cellophane thin films. The proposed mechanism was either direct excitation of the dye molecules or excitation of electrons.
In 1960, Martin Pope and co-workers at NewYork University developed ohmic dark-injecting electrode contacts to organic crystals. They further described the necessary energetic requirements (work functions) for hole and electron injecting electrode contacts. These contacts are the basis of charge injection in all modern OLED devices. Pope's group also first observed direct current (DC) electroluminescence under vacuum on a puresingle crystal of anthracene and on anthracene crystals doped with tetracene in 1963 using a small area silver electrode at 400V. The proposed mechanism was field-accelerated electron excitation of molecular fluorescence.
Pope's group reported in 1965 that in the absence of an external electric field, the electroluminescence in anthracene crystals is caused by the recombination of athermalized electron and hole, and that the conducting level of anthracene is higher in energy than the exciton energy level. Also in 1965, W. Helfrich and W. G. Schneider of the National Research Council in Canada produced double injection recombination electroluminescence for the first time in an anthracene single crystal using hole and electron injecting electrodes, the forerunner of modern...
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