Research On Improving The Efficiency Of Organic Light-emitting Devices

Up to date, Flat Panel Displays( FPDs) are playing important roles for mankind to get information and their effects are significant. Organic light emitting devices (OLEDs) are important members of FPDs and attract world wide attention in the fields of science and industry due to their many merits of light weight, low cost, broad visual angle, high response speed, spontaneous light-emitting, high brightness and efficiency, etc. Although the performances of some OLEDs are low, further improving the performances of OLEDs is still the research focus in the world. The development of OLEDs have made considerable progress. It has been started to enter the market. But how to improve brightness and efficiency is still the main focus of the research of OLED. To obtain high luminescence efficiency, we must increase the carrier injection, the balance of carrier injection and the probability of exciton formation and compound. The choose of high efficiency fluorescent materials , the use of the multi-layer structure of exciton confinement and the cathode and anode interface modification have been proved to be the most effective way to improve the device characteristics.In this thesis, we have made some meaningful works relating to the improving efficiency of OLEDs by insertion of some electrodes modification layers.1,Fabricate a organic light-emitting diode device with high electric field induced polarization of the PEDOT:PSS layer during the process of spin-coating as hole-injecting layer. The device with an appropriately treated PEDOT:PSS film exhibited significantly enhanced luminescence and decreased driving voltage. The hole-injecting and transportation ability of PEDOT: PSS was modified by applying high electric-field during the spin-coating process. The electric treatment may improve the contact between PEDOT: PSS layer and light-emitting layer, leading to improvement of device performance. The interface between ITO and PEDOT: PSS may also be modified. It has been found that the EL intensity of the OLED was significantly increased. There is also a drop in turn-on voltage. Our results suggest that the electric fields affect on formation of PEDOT: PSS layer is useful for improving the device performance.2,Based on the progress of spintronic, we firstly propose that the OLEDs internal efficiency maybe also, in principle, be increased near 100% if singlet excitons are created alone in the emitting layer through applying suitable ferromagnetic materials to control the spin direction of injected electrons and holes. We have studied the spin injection of organic light emitting devices preliminarily. The organic light-emitting devices with ferromagnetic metal iron (Fe) as the spin aligner and semi-transparent anode are fabricated. And we also insert a thin layer of FeO_x(about 10nm) between the cathode and the active layer, and research the effect of magnetic field on the performance of the device. We also realize the that to get good spin injecting efficiency organic materials with high mobility, low temperature and strong magnetic field are needed.