Electron transport materials (ETM) mainly transport electrons, and are responsible for transporting electron carriers from the metal cathode and injecting them into the light-emitting layer. The performance of ETM has a greater impact on the efficiency of OLED devices. ETM, which can greatly improve the efficiency of OLED devices, usually has the following characteristics: 1) The process of electron conduction in organic thin films is a series of redox processes, so the material must have electrochemical reduction reversibility; 2) The HOMO and LUMO energy levels of the material are appropriate to minimize the electron injection energy barrier, have a lower turn-on and working voltage, and also have hole blocking capabilities; 3) The electron mobility of the material is high, so as to ensure that the electrons can recombine in the light-emitting layer, so that the rate of exciton generation is increased; 4) The glass transition temperature (Tg) and thermal decomposition stability of the material are high, which can avoid the influence of Joule heat generated by the device during operation on the life and efficiency of the device; 5) The material should be in the form of an amorphous film, so as to avoid light scattering or decay caused by crystals. In OLED devices, common ETMs are mainly metal complexes, nitrogen-containing five-membered heterocycles, triazines, quinolines, organic boron and organic sulfur materials.
Figure 1. The position of electron transport material (ETM) in the structure of organic light-emitting diode (OLED) materials
- Organic Light Emitting Diode (OLED) devices: OLED materials are widely used in photoelectric fields such as displays, lighting, and drivers due to their high efficiency, low driving voltage, fast response time, and large-size flexible panels. In order to improve the device life and luminous efficiency of OLED materials, it is possible to start by changing the functional materials or the device structure. ETM plays an important role in OLED devices. It determines the transport capacity of carriers in the device and the position of the light-emitting layer, and is closely related to the lifespan, power consumption, and luminous efficiency of the OLED. ETM with good performance is conducive to the injection and transfer of charges. On the one hand, it is conducive to reducing the starting voltage of the device and reducing power consumption. On the other hand, it can improve the luminous efficiency of the device.
- Organic Optical Conductor (OPC): OPC is a special OLED material. OPC material can be coated on the surface of conductive metal to form a photoelectric conversion device, which can be used as the core component of laser printing and digital copying. OPC is generally composed of ETM and light guide materials. The introduction of ETM is conducive to improving the electron mobility of the material, so that the OPC material has high photosensitivity and durability.
- Dongdong Zhang,Xiaozeng Song,Haoyuan Li,Minghan Cai,Zhengyang Bin,Tianyu Huang,Lian Duan. High-Performance Fluorescent Organic Light-Emitting Diodes Utilizing an Asymmetric Anthracene Derivative as an Electron-Transporting Material [J]. Adv. Mater., 2018, 30(26), 1707590.