Analysis on the Principle of Organic EL Luminescence
The light-emitting principle of organic EL is very similar to that of LED. After voltage is applied to the cathode and anode of the material, movable electrons and cations are generated between the two electrodes. Due to the action of the electric field, the electrons and cations move to the anode and the cathode respectively, leave the two poles, and combine in the middle layer (light emitting layer) of the composite material. The combination of electrons and positrons is the energy generated so that the outermost electrons of the material are excited and cross to the outer electron orbitals. Because it is only excited, the outermost electron orbit is unstable, and the outermost electron will immediately return to the original orbit, which will release the excess energy in the form of light. From this point of view, organic EL and LED are the same. It's just that the material of organic EL is composite material, that is, multiple materials are stacked together in thin films. The cathode material is a metal that easily releases electrons, mostly aluminum, silver-magnesium alloy, calcium and other metal films; the anode is an oxide that can release cations, such as ITO, a transparent metal oxide film.
Luminescent material and production method
The main part of organic EL is the light-emitting material layer. After many experiments, the light-emitting material can be roughly divided into two categories: polymer compounds and low-molecular compounds.
Low-molecular luminescent materials mainly include fluorescent materials and phosphorescent materials.
Fluorescent materials are easy to produce three primary colors (red, green and blue). In addition, the price, lifespan, and processing are very convenient. It is a preferred low-molecular luminescent material. The luminous efficiency of phosphorescent materials is much higher than that of fluorescent materials, but the luminous efficiency decreases with the increase of current, the life is not long, the purification is difficult, and the blue spectrum is not as complete as the fluorescent materials. Research and development are still needed.
Compared with high-molecular luminescent materials, the biggest problem of low-molecular luminescent materials is the difficulty in processing and manufacturing. Especially can not cope with large-scale production. Since the materials are attached to the surface of glass or transparent polymer in the form of a thin film, the thin film technology and surface treatment technology of polymers far exceed those of low molecules. In addition, the potential of polymer luminescent materials is also very large, and continuous experimental research will produce many new materials.
Because organic EL is thin and light, its material must be attached to the substrate through thin film processing. This requires the use of surface treatment technology. In Japan, the core of thin film technology and surface treatment technology is held by large-scale printing companies (Dainippon Printing, letterpress printing, etc.). Through CVD, PVD and other thin film attachment methods, various polymer materials can be attached to the substrate. The improvement of adhesion technology can also realize large-area organic EL.