The materials used in OLED display screens are mainly divided into cathode materials, anode materials, buffer layer materials, carrier transport materials, and light-emitting materials. The following will introduce their main functions

1. Cathode material

The cathode material of the OLED is used as the cathode of the display screen. In order to improve the injection efficiency of electrons, a metal material with a work function as low as possible should be selected because the injection of electrons is more difficult than the injection of holes. The size of the metal work function seriously affects the luminous efficiency and service life of the OLED device. The lower the metal work function, the easier the electron injection, and the higher the luminous efficiency. In addition, the lower the work function, the more organic / metal interface barrier. Low, the less Joule heat generated during work, the greater the life of the device.

2. Anode material

The anode material of OLED is mainly used as the anode of the 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 be transparent, so ITO conductive glass, which is a transparent material with a high work function, is usually used as the anode. ITO (indium tin oxide) glass has a transmittance of more than 80% in the wavelength range of 400nm to 1000nm, and also has a high transmittance in the near ultraviolet region.

3. Buffer layer material

In OLEDs, the transport rate of holes is about twice the transport rate of electrons. In order to prevent the quenching of light caused by the transport of holes to the organic / metal cathode interface, a buffer layer CuPc needs to be introduced when preparing the device. CuPc as a buffer layer can not only reduce the interface barrier between the ITO / organic layer, but also increase the degree of adhesion at the ITO / organic interface, increase the hole injection contact, inhibit the injection of holes into the HTL layer, and make electrons and The injection of holes is balanced.

4. Carrier transport material

OLED devices require that the holes injected from the anode and the electrons injected from the cathode be injected into the light-emitting layer in a relatively balanced manner, that is, the hole and electron injection rates should be basically the same. Therefore, it is necessary to select a suitable hole and electron transport. material. During the operation of the device, the heat may cause the transmission material to crystallize and cause the performance of the OLED device to deteriorate. Therefore, we should choose a material with a higher glass transition temperature (Tg) as the transmission material. In the test, NPB is usually used as the hole transport layer, and Alq3 is used as the electron transport material.

5. Luminescent materials

Luminescent materials are the most important materials in OLED devices. General luminescent materials should have high luminous efficiency, preferably have electron or hole transport properties, or both. They can be made into stable and uniform films after vacuum evaporation. Their HOMO and LUMO energy should match the corresponding electrodes. And other characteristics. Among the small-molecule light-emitting materials, Alq3 is a material used directly as a light-emitting layer alone. There is also that it cannot be used alone as a light-emitting layer, and it can emit light only when it is doped in another host material, such as red light dopant DCJTB, green light dopant DMQA, blue light dopants BH1, BD1 and so on. Alq3 is an organic material that can be used as both a light-emitting layer material and an electron transport layer material.