Abstract
OLED (Organic Light Emitting Diode) devices, which are receiving attraction as next generation FPDs (Flat Panel Displays) and lighting devices, suffer from the problem of having a short lifetime. The relationship between lifetime and brightness represents a trade-off. A mechanism for improving durability and extending lifetime is necessary in order to create a bright and stable device. Therefore, it is important to ascertain the causes by which application of voltage leads to deterioration of OLEO devices. It is considered that one of the causes of deterioration of the device is a chemical change in the interface between the electrode and organic layer that occurs when a voltage is applied. In this research, the authors investigated the chemical change in the interface between the electrode and organic layer that occur when a voltage is applied. The structure of device used in this research consisted of CuPc (Copper Phthalocyanine) formed between ITO (Indium Tin Oxide) and aluminum. We analyzed the chemical composition of the device using XPS (X-ray Photoelectron Spectroscopy) after peeling off the aluminum cathode with carbon tape and compared chemical condition in the interface between CuPc layer and ITO anode before and after applying voltage. The results of this analysis show that indium, which was not detected before applying voltage, was detected in the CuPc layer on the substrate side after applying it. Therefore, there are possibilities that the ITO, located under the CuPc layer, appeared because the adhesion between the ITO and CuPc layer had become weak or the adhesion between the aluminum and CuPc layer had become strong. In addition, indium was also detected in the CuPc layer on the carbon tape side after applying voltage. Therefore, two possibilities are considered as the cause of these results. One is diffusion of the ITO into the CuPc layer and the other is some chemical change occurring between the ITO and the CuPc. We consider that these results cause decrease of the OLED lifetime in the early stage.
