The basic structure of OLED is a thin and transparent indium tin oxide (ITO) with semiconductor properties, which is connected with the positive electrode of the electric power, plus another metal cathode, which is wrapped into a sandwich structure. The entire structural layer includes: a hole transport layer (HTL), a light-emitting layer (EL) and an electronic transport layer (ETL). When the power supply to the appropriate voltage, the cathode hole and the cathode charge will be in the light-emitting layer combined to produce light, according to its formula to produce red, green and blue RGB three primary colors, constitute the basic color. OLED characteristics are their own light-emitting, unlike Tft LCD need backlight, so visibility and brightness are high, followed by low voltage and high efficiency, coupled with quick reaction, light weight, thin, simple structure, low cost, is considered as one of the most promising products in the 21st century.
The luminescence principle of the organic light-emitting polar body is similar to that of the inorganic light-emitting dipole. When the component is subjected to a direct bias derived from the DC (direct CURRENT;DC), the applied voltage energy will inject the drive electron (electron) and the Hole (Hole) respectively by the cathode and the anode, and when the two meet and bind in conduction, the so-called electron-hole recombination is formed ( Electron-hole Capture). And when the chemical molecule is stimulated by foreign energy, if the electron spins (electron Spin) and the ground state electron pair, it is a single (singlet), the light emitted by the so-called fluorescence (fluorescence), and conversely, if the excited state electrons and the ground states electron spin is not opposite and parallel, It is called a triple State (Triplet), and the light released by it is called phosphorescence (phosphorescence).
When the state position of the electrons is returned to the steady-state low-energy order by the high-energy order of the excited state, the energy of the electron is emitted in the form of photons (Light emission) or thermal energy (Heat dissipation), in which the part of the photon can be used as the display function; However, the organic fluorescent material can not observe the three-state phosphorescence at room temperature, so the theoretical limit value of the luminous efficiency of the pm-oled element is only 25%.