ORGANIC LIGHT EMITTING DEVICES WITH DIAMOND ELECTRODES

摘要

In this paper, Organic light emitting devices with diamond electrodes were investigated. Experimental studies showed that the stability of the organic light emitting devices with diamond electrodes was greatly improved in comparison with the devices based on metal electrode. Since the observation of electroluminescence in poly (P-phenylene vinylene) (PPV), there has been considerable interest in utilizing organic light emitting devices for the application of full color flat panel display, field effect electro-optical modulators, light detectors, sensors and photo- detectors. This is due to that the organic materials offer numerous advantages for easy processing, good compatibility with a variety of substrates including flexible plastics and low costs. But, there are still several problems concerning the stability and reproducibility of device fabrication. As an example, an organic light emitting device made using tris-(8-hydroxyquinoline) aluminum (Alq_3) as the active electroluminescence layer lost 50% of its initial electroluminescence intensity in 100h when it operated in dry Ar at a drive current of 5mA/cm~2. According to recent studies, these devices fail because of exposure to oxygen, moisture, high electric field and high intensity illumination, leading to electrochemical reaction on interfaces of the electrodes. As a result, the electrode materials are not only degraded, but they also form a complex with the bulk organic materials, which serves as a "weak electrolyte". In the paper, the stability and lifetime of organic light emitting device are investigated by impedance spectroscopy, electrochemical measurement and scanning electron microscopy. To minimize the effect of metal materials, the devices were produced using heavily born doped diamond films as the conducting electrode in place of the aluminum. Experimental results showed that the stability of device was greatly improved.