The main material composition of OLED display screen

by:Genyu     2019-11-27
The materials used in OLED display screen are mainly divided into cathode materials, anode materials, buffer layer materials, carrier transport materials and luminescent materials according to their functions. The following will introduce their main functions 1. Cathode material the cathode material of OLED is used as the cathode of the display screen. In order to improve the injection efficiency of electrons, metal materials with the lowest work function as far as possible should be selected, because the injection of electrons is more difficult than the injection of holes. The size of metal work function seriously affects the luminous efficiency and service life of OLED devices. The lower the metal work function, the easier it is to inject electrons and the higher the luminous efficiency; In addition, the lower the work function, the lower the organic/metal interface barrier, the less Joule heat generated during operation, and the longer the device life. 2. Anode material the anode material of OLED is mainly used as the anode of display screen, and its work function is required to be as high as possible in order to improve the hole injection efficiency. OLED devices require that one side of the electrode must be transparent, so ITO conductive glass, a transparent material with high work function, is usually selected as the anode. ITO (Indium tin oxide) Glass at 400nm ~ The transmission rate is above 80% in the wavelength range of 1000nm, and it also has high transmission rate in the near ultraviolet region. 3. The transmission rate of the buffer layer material in the OLED cavity is about twice that of the electron transmission rate. In order to prevent the quenching of light caused by the hole transmission to the organic/metal cathode interface, buffer layer CuPc should be introduced when preparing devices. CuPc, as a buffer layer, can not only reduce the interfacial barrier between ITO/organic layers, but also increase the adhesion degree of ITO/organic interfaces and increase hole injection contact, the injection of holes into HTL layer is inhibited to balance the injection of electrons and holes. 4. Carrier transport material OLED devices require holes injected from the anode and electrons injected from the cathode to be injected into the light emitting layer in a relatively balanced way, in other words, it is required that the injection rates of holes and electrons should be basically the same, so it is necessary to select suitable holes and electron transport materials. In the working process of the device, since heating may cause crystallization of the transmission material, resulting in attenuation of OLED device performance, we should choose the glass transition temperature (Tg)Higher materials are used as transmission materials. In the experiment, NPB is usually selected as the hole transport layer, while Alq3 is selected as the electron transport material. 5. Luminescent materials, luminescent materials are the most important materials in OLED devices. Generally, luminescent materials should have high luminous efficiency, preferably electron or hole transport performance or both, stable and uniform films can be made after vacuum evaporation, and their HOMO and LUMO energies should be corresponding the electrode matching and other characteristics. Among small molecule luminescent materials, Alq3 is a material directly used alone as a luminescent layer. Another thing is that it cannot be used as a light-emitting layer alone and can only emit light when doped in another matrix material, such as red light dopant DCJTB, Green Light dopant DMQA, blue light dopant BH1, BD1, etc. Alq3 is an organic material that can be used as both a luminescent layer material and an electron transport layer material.
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