Polymer Carrier Injection And Transport Properties Of The Light-emitting Devices

Polymers are used as the light-emitting layer in Polymer light-emitting devices(PLED). Because of the good mechanical property, high thermal stability, the convenience of fabrication and the potential application in large-area flat panel display at low power consumption, study on PLED for the new generation in panel display have been a hot topic all over the world.The process of carrier injection is one of the most fundamental physical processes in PLED. It can affect many important properties of PLED. To improve the injection of electron in cathode, an insulating layer is often used between the polymer layer and cathode. In order to know the electron injection characteristics of the interface when the insulating layer thickness is changed. we have made PLED with the MEH-PPV as light-emitting layer and LiF as insulating layer material. When the thickness of LiF under common voltage changed, the current of electron injection increase at first and then decrease, which suggest there is an optimum thickness of the insulating layer when the barrier of electron decrease most.In order to investigate the electron injection properties of different insulating material, we study the I-V characteristics of PLED with ZnS,BaO,MgF₂ as multiple cathode . Our study results show the material with a lower dielectric constant is better.In the emissive layer, most polymer is in amorphous state. The amorphous state for polymer in the emissive layer and the impurities brought by the polymer synthesizing process, which both cause many defects and traps in the emissive layer. Carriers can be caught by these traps, which have important effects on the performance of PLED. According to some calculating model, we have tested and calculated several models about the electron injection of PLEDs, the result show the change of the organic layer have an obvious affect the trap density ,while the change of the insulating layer have weak effect on the trap density...