Based On Mixing The Main Doping Red Organic Light-emitting Devices

Organic light-emitting diode(OLED) has become an important research area due to its potential applications in flat panel displays field. For full color display, the high luminescent intensity and pure red, green and blue OLEDs have been investigated intensively in recent years. So far, the reported blue and green OLEDs have shown sufficient performance for commercial displays. However, the performance of red OLEDs still need to be improved. The doped red OLED based on mixed host (MH) is fabricated and studied in this dissertation. In order to understand the physical mechanism involved in OLEDs, the injection and transport properties of single-layer and double-layer devices are simulated.The Electroluminescence and I-V properties of the doped red OLED based on MH are studied, the devices' structure is designed as: ITO/PVK: Alq: DCM (0.8wt%) /Alq/Al. The luminescent intensity achieves the highest and the operating voltage achieves the lowest when the weight ratio of PVK and Alq is 1:1. Compared to the single host device, The luminescent intensity of mixed host device is 25% higher and the drive voltage 3.2V lower.The MH devices' CIE coordinate under different voltages is shown superposed in the chromaticity diagram, which proves that the MH devices can produce steady, saturated and high luminescent intensity red emission. The superior performance is attributed to the electron-hole bipolar transport characteristic of mixed host, which helps to blur the emitting layer (EML)/electron transport layer(ETL) interface and reduce the carrier accumulation. The research offers powerful and meaningful preference for the development of red OLEDs.The charge transport of the the single-layer OLED made of Alq is discussed by the F-N tunneling model. The I-V curve shows rectification characteristics, which makes clear that the current of the OLED is injection-limited when the injection barrier is high. The carrier mobility is proven to be insensitive to the positions in our device, but temperature and electric field have strong influence on carrier mobility.The simulation of the electric field distribution in the device and J-V properties of double-layer OLEDs made of PVK and Alq is also fulfilled in this research work. The models used here are the space charge-limited current without trap and trap-charge limited current.Our simulation results show that the electric field is discontinuous, and TCLC is better fit to the measured data than SCLC due to the existence of trap in organic films. These works may help to have an insight into the operating principle of OLED.