An organic light emitting diode (OLED), also light emitting polymer (LEP) and organic electro luminescence (OEL), is any light emitting diode (LED) whose emissive electroluminescent layer is composed of a film of organic compounds. The layer usually contains a polymer substance that allows suitable organic compounds to be deposited. They are deposited in rows and columns onto a flat carrier by a simple "printing" process. The resulting matrix of pixels can emit light of different colors.
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An organic light emitting diode (OLED), also light emitting polymer (LEP) and organic electro luminescence (OEL), is any light emitting diode (LED) whose emissive electroluminescent layer is composed of a film of organic compounds. The layer usually contains a polymer substance that allows suitable organic compounds to be deposited. They are deposited in rows and columns onto a flat carrier by a simple "printing" process. The resulting matrix of pixels can emit light of different colors.
Such systems can be used in television screens, computer displays, small, portable system screens such as cell phones and PDAs, advertising, information and indication. OLEDs can also be used in light sources for general space illumination, and large-area light-emitting elements. OLEDs typically emit less light per area than inorganic solid-state based LEDs which are usually designed for use as point-light sources.
A significant benefit of OLED displays over traditional liquid crystal displays (LCDs) is that OLEDs do not require a backlight to function. Thus they draw far less power and, when powered from a battery, can operate longer on the same charge. Because there is no need for a backlight, an OLED display can be much thinner than an LCD panel. Degradation of OLED materials has limited their use so far.
History
A. Bernanose and co-workers at Université de Nancy, France, first produced electroluminescence in organic materials in the early 1950s by applying high-voltage alternating current (AC) fields in air to acridine orange and quinacridine either deposited on or dissolved in cellulose or cellophane thin films. They proposed a mechanism of either direct excitation of the dye molecules or excitation of electrons.
In 1960, Martin Pope and his group made the seminal discovery of ohmic, dark injecting electrode contacts to organic crystals, and described the necessary energetic requirements (work functions) for hole and electron injecting electrode contacts. Dark injecting hole and electron injecting electrode contacts are the basis of all current OLED devices, molecular and polymeric, as will be pointed out in the description of the requirements for the construction of successful OLEDs.
In 1963, Martin Pope and his group made the first observation of direct current (DC) electroluminescence, under vacuum, on a pure, single crystal of anthracene, and also on anthracene crystal doped with tetracene. The injecting electrode was a small area silver electrode, at 400 V DC, and the proposed mechanism was field accelerated electron excitation of molecular fluorescence.
In 1965, Martin Pope and his group refined their experiment and showed that in the absence of an external electric field, the electroluminescence in anthracene single crystal was caused by the recombination of a thermalized electron and hole. This paper proved conclusively that the conducting level of anthracene is higher in energy than the exciton energy level.
