Application Of The Ultra-thin Layer In Organic Light-emitting Devices

Up to date, Flat Panel Displays (FPDs) are playing important roles for people to get information. Organic light emitting device (OLED) as one of the major Flat Panel Displays has attracted world wide attention due to their merits of light weight, low cost, broad visual angle, high response speed, spontaneous light-emitting, high brightness and efficiency, etc. Although much progress has been made on OLEDs, further improvement of the performance of OLEDs is still the research focus in the world. In this dissertation, main study is on device structure, performance and luminescence mechanism etc. of OLEDs. Some interesting results have been obtained.1. The effect of ozone and O₂ plasma treatment of ITO on the charge-carrier injection in ITO/NPB/AlQ/Al organic heterojunction devices have been studied through the analysis of current-voltage characteristics. From the experiments, it is demonstrated that the average electric field inside AlQ layer is larger than the average field in the NPB layer. The investigation demonstrated that the hole injection into NPB from anode is Fowler-Nordheim (FN) tunneling and the electron injection into AlQ from cathode is Richardson-Schottky (RS) thermonic emission.2. The effect of the thickness and position of the thin DCJTB layer on the performance of the devices has been investigated. The EL peak emission of DCJTB shifted to blue with the position of thin DCJTB layer moved from near the NPB/AlQ interface in AlQ layer to the ITO anode. A white emitting device has been made with the structure of ITO/NPB(45 nm)/DCJTB(0.15 nm)/NPB(5 nm)/DCJTB(0.15 nm)/BCP(10 nm)/AlQ(50 nm)/LiF(0.3 nm)/AI(150 nm). This device exhibited a pure white-light emission having CIE coordinates of (0.324,0.336) at the current density of 100 mA/cm², a current efficiency of 2.9 cd/A.3. The thin rubrene layer has been adoped as the emitting layer and the effect of the thickness and position of the rubrene layer on the performance of the devices has been studied. When the layer of rubrene is 4-5 nm away from the NPB/AlQ interface, the emission of rubrene will dominate more than 80 percent of the intensity in the EL spectrum of the device. The rubrene layer has been used as the "helper layer" in the fabrication of the red emitting devcies based on DCJTB layer. The results show that both efficiency and brightness are highter than that of the device without the rubrene layer and the CIE coordinate of the device is stable with the voltage.4. The property of the interface is critical for the performance of the OLEDs. An interfacal layer of PMMA has been made at the interface of the hole injecting layer of PEDOT:PSS and the emitting layer of MEH-PPV by spin-coating. From the results, we found that the efficiency of the device with 3 nm PMMA layer is about two times of the device without PMMA layer.