1. The history of luminescence What is luminescence (EL, Electro Luminesence) Electro Luminesence (EL) was first discovered by Dr. Destria in 1936. It is a technology with a history of sixty years. Until recently, due to solid-state chemistry and thin-film semiconductors With the development of technology, EL flat panel displays have gradually received attention. EL can be divided into organic and inorganic according to luminescent materials. In the past, most of the researches were based on inorganic. At present, organic electroluminescent materials have reached industrial value after a breakthrough in their operating life. EL can be applied to various OA devices such as word processors, personal computers, and navigation terminals for vehicles. In addition, the full-color EL display has reached a practical level, and in the near future, it is eager to improve the high-definition full-color EL display. Due to the development of information technology, flat panel displays (FPD) have gradually become the mainstream of electronic application products, such as various electrical appliances in daily life, including; TVs, car dashboards, watches, advertising billboards... etc. . At present, there are three types of flat-panel display technologies, namely, liquid crystal display (LCD), plasma display panel (PDP) and electroluminescent display (ELD). The liquid crystal display is low in cost and consumes electricity. The volume is small, and it has been widely used in portable computers. However, the liquid crystal type still has many shortcomings, such as poor viewing angle, slow speed, complex structure, inability to enlarge and high production cost, etc., and the visual display of electroluminescent display Angle, light emission but no heat, flexible screen, thin and short, etc., make EL flat panel displays have great development potential in the future. Electron luminescence (EL) is a physical phenomenon that converts electrical energy into light energy. EL was first discovered by German scientist Dr. Destria in 1936. The luminescence phenomenon is produced by immersing a zinc sulfide (ZnS) rod in a mercury electrode. However, there was no discovery of a transparent electrode at that time, so it was not until the discovery of a transparent electrode in 1951. Indirectly promotes the design of EL as a flat light source. However, due to the problem of the luminous intensity and lifetime of EL, EL still cannot be applied in practice. In 1974, Inoguchi published a thin-film EL structure with double insulating layers, which solved the problems of luminous intensity and lifetime, and only then began to become a new field of research. Table 1-1 shows the development history of EL flat panel displays. The term flat panel display first appeared in the 1960s, and it has been developed to this day. There are currently two companies, Sharp in Japan and Planar systems in the United States. The latter is a subsidiary of Tektronix established in 1983. 240'Sharp first introduced the monochrome 320 240'EL display in 1983, and the first generation of portable computers used this display. Planar of the United States launched a full-color ACTFEL (AC-driven thin-film type) 320 dots flat-panel display in 1988, which attracted considerable attention from the display industry. Now Planar systems has completed the commercialization of multi-color EL displays, and the first full-color EL prototype was sampled in 1993. EL is a simple and reliable way of luminescence. It is a technology with a history of 60 years. However, it has not been paid attention to since its development because of the more complex solid-state chemistry and material applications. In recent years, the solid-state technology has become more mature. It will occupy an important market in the future. 2. Principle The basic structure of ELD is shown in Figure 2-1. It mainly includes electrode materials, insulating materials and luminescent materials (phosphors). Phosphor materials are usually divided into two types: organic and inorganic. There are many inorganic researches. EL is similar to a semiconductor, and the fluorescent body is mainly composed of a luminescent center formed by a host material (Host) and an appropriate additive (Dopant, also known as Activator). At present, most of the parent materials that have been developed are ionic compounds of group Ⅱ-VI, which roughly include Ca, Sr, Ba (group ⅡA) or Zn, Cd, Hg (group ⅡB) with S, Se (group Ⅵ) ) As the parent material. Additives determine the color of luminescence. Generally, the additives are Mn, Cu, Ag, and lanthanide elements (Eu, Sm, Tb) and other transition metals. Table 2-1 is based on zinc sulfide as the parent material and adding different activators. Luminous color; because the luminescence mechanism involves the filling of cation holes, if the additive is not a divalent metal, a monovalent or trivalent substance for charge balance must be added, usually halogens such as F, Br, Cl, etc., this charge balance substance Known as the co-activator (Co-activator). The formation of EL light requires an applied voltage above 10V/cm. This article will explain the relationship between the applied voltage, the brightness of the EL component and the luminous efficiency. Figure 2-3 shows the relationship between the brightness, luminous efficiency and the applied voltage of the EL component. In the picture, the picture can be divided into three regions. The first region is the low voltage region (I). Because the applied electric field is very low, the conduction electrons cannot excite the outer electrons in the light-emitting center, and the EL component will not emit light; when the voltage reaches In the medium voltage region (II), the conduction electrons are accelerated into hot electrons, which can excite the luminous center, and the EL component will produce luminescence. At the same time, in this area, the increase of the electric field causes the energy of the hot electrons to increase sharply, resulting in an increase in luminous intensity and efficiency. ; Finally, when the voltage reaches the high voltage area (Ⅲ), the hot electrons in the light-emitting layer will cause insulation damage, so the increase of the applied electric field will no longer cause the electric field in the light-emitting layer to rise, and the energy of the hot electrons will not increase. The luminous efficiency also remains constant. Comparison of organic EL and inorganic EL 1. What is OEL OLED Organic EL is ORGANIC ELECTRO LUMINESCENT for short OEL, OLED is ORGANIC LIGHT EMITTER DEVICE and organic EL, OEL are the same but the name is different 2. Organic EL and inorganic EL, the principles are both It is the same. The light-emitting layer between the two ends plus electrodes is excited to emit light, but the raw material of the inorganic light-emitting layer and the guest luminous material (DOPANT EMITTER MATERIAL) use inorganic substances such as ZnS, Cu, Mn, etc., while the organic EL uses organic Compounds as luminescent materials and guest luminescent materials such as PPV, CN-PPV, PVK. 3. Organic EL (OLED) is divided into small molecule (MOLECULES) EL and polymer (POLYMER) EL. Please refer to the attached table for its characteristics. 4. Inorganic EL is easy to process and low in cost, but the color change is not easy to control and its DRIVER voltage High, low operating voltage of organic EL (below DC 10V), so the control circuit is easier to manufacture, and the color control of organic EL is easier. The initial investment of organic EL is large. Because the process is useful for evaporation, it is more difficult for large-size ones, and organic EL materials currently have patents, so organic EL manufacturing is owned by major manufacturers, such as Kodak, PHILIP, PIONEER, etc. To produce organic EL, Taiwan’s factories must overcome initial investment funds and obtain patent authorization, so the obstacles are very high. Big.
