Research Of The Performance And Mechanism Of Organic Light-emitting Devices

Since the efficient organic light emitting device (OLED) was reported in 1987, it has been applied widely and considered for next generation flat panel display after CRT and LCD during to their various advantages such as low drive voltage, wide visual angle great, fast response and simple fabrication. At the present time, the primary aims of study work are exploiting organic light-emitting and carriers transporting materials with high EL efficiency and stable physic characteristics, searching for new film fabrication technics, and optimizing device configuration. This paper summarizes and introduces the research in my master period, accompanied by the national Natural Science Foundation of China (NO.60276033). The key points are listed blow: study of fabrication technics and characteristics of blue light-emitting devices and white light-emitting devices; improvement mechanism is analyzed on the base of the synthesis of electrode study; stability and invalidation mechanism of OLED are also described in this paper. The analyses are listed blow:1. From the characteristics of the device ITO/PVK:TPD/BA/Alq₃/Al, it is found that the current is increased with drive voltage, which indicates a diode characteristic. When the voltage is under 10V, there is almost no current, and the current increased quickly while the drive voltage is higner than 13V. The open voltage is 7.5V, and the luminescence brightness is 1042cd/m² when the drive voltage increases to 22V.2. A white organic light emitting device (OLED) with a single layer consisting of an orange-red dopant 5,6,11,12-tetraphenylnaphthacene (rubrene) and a blue light emitting material 8-hydroxyquinoline lithium (Liq) mixed with a certain proportion was fabricated. While the proportion is 1.1%, the Commission International De L'Eclairage(CIE) coordinate of device is (0.308,0.347).The driving voltage of device is 8V, and luminescence brightness is 3024cd/m² when the voltage is increased to 25V.3. Improvement mechanism of electrode is also studied based on the synthesis of research process of electrode. To the anode material ITO, Carbon pollution is the main infection to the work function of ITO. Moderate oxygen plasma disposal is an ideal method relatively, which is not only can increase ITO work function but also reduce the resistivity, and the square resistance is decreased. To cathode material, alloy electrode, Al/LiF double layer electrode and compound electrode are thought to be well. A thin insulator layer is added in metal/insulator electrode to improve electron injection efficiency, and this paper has analyzed the three kinds of explanations to the improvement of equilibrium condition of electron and hole.4. The degeneration mechanism of OLED is described detailedly. The degenerations are mainly from the crystallization, diffusation, oxidation, and decomposition of orgnic layer and the formation and growth of dark spot. The proper anneal could form an interface layer between electrode and organic layer, which enhance the conglutination between the two layers, and increase the efficient area for electrons injection. Moreover, the formation of interface layer could help to holding up holes, and decrease the quenching of excitons, which increase the probability combination of electrons and holes. So the luminescence efficiency of device is improved.