Organic light-emitting diode (OLED) is a highly efficient semiconductor device for converting electrical energy into optical energy. The organic light emitting diode utilizes an emissive characteristic organic film between two electrodes. When the direct currency voltage is charged to the electrodes, a hole will be injected from the anode, and an electron will be injected from the cathode. A basic structure of the organic light emitting diode includes a glass substrate, a metal electrode, an indium-tin-oxide (ITO) electrode and an organic emitting layer. In the emitting principle of the organic light emitting diode, the metal electrode is a cathode and the indium-tin-oxide is an anode. When the forward bias is charging on the two electrodes, an electron and a hole are respectively injected from the metal electrode and the ITO electrode into the emitting layer. When two carriers meet in the emitting layer and produce a photon by a radioactive recombination and a light emitting phenomena is achieved. In an OLED, in each case one of the conductive layers acts as a cathode and the other as an anode. For this purpose, it is known to make the electrode layers from materials with different work functions, so that a work function difference is formed between these layers. Organic light-emitting diodes which can realize full-color display devices are largely divided into two types according to the organic material used: OLEDs employing low molecular materials; and OLEDs employing polymer high molecular materials. A high molecular OLED is generally fabricated such that two opposite electrodes (a cathode and an anode) are disposed on a substrate, and a hole transport layer (HTL) and an emission layer are provided between the anode and the cathode. In the polymer high molecular OLED, the HTL and the emission layer are formed of organic polymers.

Light-emitting diodes comprising luminous layers of organic materials are clearly superior to light sources of inorganic materials. One advantage is that they can be readily moulded and exhibit a high elasticity, thus enabling new applications for luminous displays and display screens. These layers can be readily manufactured as large-surface, flat and very thin layers for which, in addition, only a small amount of material is necessary. Said layers are characterized by a remarkably high brightness in combination with a small drive voltage. LEDs with organic thin films are attractive because such devices need not be produced on a crystalline substrate, the cost of producing such devices is low, the devices operate at low voltage, and the organic thin films enable devices that emit light in a variety of colors to be produced. Organic light emitting diode (OLED) is a semiconductor device capable of converting electrical energy into light energy with a high conversion efficiency. An optoelectronic device converting optic energy into electric energy vice versa is very important in the electronic information industry nowadays. Because OLED has some special properties such as wide viewing angle, ease of manufacture, low production cost, high response speed, wide range of operating temperature and full coloration, OLED is a suitable candidate for forming multimedia display devices. Organic light emitting diode (OLED), is useful in flat-panel display applications. This light-emissive device is attractive because it can be designed to produce red, green, and blue colors with high luminance efficiency; it is operable with a low driving voltage of the order of a few volts and viewable from oblique angles. These unique attributes are derived from a basic OLED structure comprising of a multilayer stack of organic thin films sandwiched between an anode and a cathode.

Flat panel displays have become important elements in electronic products such as notebook computers, televisions and others. The passive-matrix liquid-crystal displays (LCDs) and active-matrix liquid crystal displays (AMLCDs) have become dominant in display applications. However, LCDs fail to provide the bright, high light output, larger viewing angles, and high resolution and speed requirements that the large-screen display market demands. By contrast, OLED technology promises bright, vivid colors in high resolution and at wider viewing angles. Demands for large-screen display applications possessing higher quality and higher resolution has led the industry to turn to alternative display technologies that replace older LED and liquid crystal displays (LCDs). Owing to high brightness, fast response speed, light weight, thin and small features, full color, no viewing angle differences, no need for an LCD back-light board and low electrical consumption, an organic light emitting diode display or organic electroluminescence display (OLED) takes the lead to substitute a twist nematic (TN) or a super twist nematic (STN) liquid crystal display. Since a backlight does not need to be provided in conjunction with such OLED devices, the size and weight of OLED devices are small, as compared to other types of display devices. Because OLED devices are entirely formed of materials in a solid phase arrangement, unlike LCD devices, OLED device are sufficiently strong to withstand external impacts and also have a greater operational temperature range. The driving method for the OLED includes a passive type and an active type, the active type is suitable for achieving a large-screen and high-definition display in light of aspects involving a material, a life, and crosstalks. This active type requires thin film transistor (TFT) driving, and a TFT array applying low-temperature polysilicon or amorphous silicon (a-Si) is drawing attention for this use.