OLED has the advantages of active light emission, easy realization of large-screen flexible display, continuous adjustment of light emission color, easy realization of blue light emission, wide viewing angle, simple process, low cost, etc., and has significant applications in many fields. The OLED device is composed of a cathode, an anode, and an organic layer in the middle. The organic layer generally includes an electron transport layer, a light emitting layer, and a hole transport layer. In OLED materials, the host material usually contains a hole and/or electron transport layer, which has suitable carrier transport properties, and its triplet energy level is higher than that of phosphorescent emitters, which can confine the triplet excitons to the light-emitting layer. The host material affects the luminous efficiency of the entire device. In OLED devices, host materials play a vital role. The state of the organic molecules in the OLED device is a thin film state, and the organic material in the thin film state will produce a concentration effect due to the interaction between the molecules, resulting in a sharp drop in the efficiency of the device. Therefore, in general, in an OLED device, doping the guest light-emitting material into the host material can reduce the interaction between the light-emitting molecules, alleviate the concentration quenching effect, and improve the light-emitting efficiency of the OLED device. It can be seen that the host material plays a vital role in OLED devices and affects the application of OLED materials.
Figure 1. The molecular structure of some OLED host materials