Research Of The Performance And Failure Mechanism Of Organic Light-emitting Diodes

The organic light-emitting diode (OLED) has lots of advantages, such as high efficiency (energy conservation), light and thin, wide viewing angle, lifelike colors, flexible display, shock-resistant and so forth, therefore, it is called dream display technology. In recent years, researchers all over the world have been trying their best to study and develope the OLED. People think that it has excellent application prospect.This paper presents the OLED’S research situation at present and development trend in the future, introduces all kinds of organic electroluminescence materials and packaging technology of OLED. The working mechanism and structures of OLED are described in detail.Using the evaporation method we got three types of samples, which are ITO/m-MTDATA, ITO/NPB and ITO/TPD on the ITO glass. Their surface morphologies are got by atomic force microscope (AFM). The m-MTDATA film is very flat according to AFM results and its HOMO energy level is lower than hole-transport materials (such as NPB and TPD), so it is a kind of excellent hole-injection material. If we use it in the OLED, the performance of device will be promoted. According to the surface morphology figure of ITO/TPD we can see that the TPD has been crystalized, which indicates that TPD is not the good choice for OLED because of its low glass transition temperature. The glass transition temperature of NPB is bigger than TPD; therefore, researchers now usually use NPB as hole-transport material. If you have to use TPD, the temperature parameter in the evaporation process must be lower than glass transition temperature.Two kinds of green OLED based on TPD and NPB respectively are fabricated successfully. According to the comparison of devices’performance we find that NPB is more suitable for OLED as hole transport material. In order to avoid the problem that the direct testing makes the device destroyed easily, we adopt the strip electrode. This kind of approach has a great meaning in enhancing the stability of OLED.The red OLED based on Alq3:rubrene:DCJTB is fabricated. The host Alq3 transfers energy to the luminescence guest DCJTB. In order to enhance the transference efficiency, the assistant rubrene is added into the Alq3:DCJTB. Because of this we get relatively saturated red light emitted. However, the turn-on voltage of OLED is still too high. When add the m-MTDATA which is a kind of hole injection material the device’s turn-on voltage decreases and the luminance increases. We adopt the approach that etching ITO to make the device radiates light stably for a long time and not degenerateAt last, the failure mechanism of the green OLED and red OLED is analyzed in detail. The most important reasons of the devices’failure are water used to clean the ITO glass is not pure enough and contamination comes from chambers and environment. The contamination particles connect ITO and Al directly, which causes the short circuit of device. Like this, large current is formed and finally the device is burned off. If the contamination particles are not conductive the surfaces having contamination particles will be insulative, which leads to the formation of black dots. Moreover, the shadow effect caused by those contamination particles can make the black dots area expanded and finally results in the mortal damage of device. During the experiments, we find that the performance of OLED will be tremendously influenced by the thickness of Al electrode. If the Al electrode is too thin (<70nm), the device will be burned off easily because of its bad ability to withstand voltage.