| In recent years, organic light emitting diodes (OLEDs) have been actively investigated due to their great potential as flat panel displays and solid-state lighting sources. To obtain high efficiency requires optimizing all the electrical and optical processes occurring within the devices.; The light coupling efficiency of a conventional OLED is less than 20%, which is a main hurdle for achieving high efficiency devices. In this thesis, an optical model is first exploited to describe the optical physics involved. Various techniques are investigated to improve the outcoupling efficiency. Employment of nanoporsous films enhances the efficiency by about 50%. Through use of microlens array the coupling efficiency is improved by 90%. Microcavity structures using either DBR or metal reflector are designed and fabricated to enhance light coupling efficiency and tune the emission color.; The ITO/organic interface plays an important role in the device efficiency and lifetime. A novel ITO pretreatment technology using carbon tretrafluoride (CF4) plasma was investigated. The devices demonstrate better performance than those using conventional oxygen plasma. Meanwhile, Ag is examined as an alternative anode and demonstrates improved hole injection ability after surface modification.; High efficiency green and red electrophorphorescent OLED using semitransparent Ag as the anode have been fabricated. The results of the green emission OLEDs show that the maximum etaext, etaJ and eta P of the Ag anode device are 18.3%, 81 cd/A and 79 lm/W, respectively, compared with those of 12.3%, 46 cd/A and 39 lm/W for the ITO anode device. For the red emission devices, the maximum etaext and eta P of the Ag anode device are 14.7%, and 18.1 lm/W, respectively, compared with those of 11.1%, 11.5 lm/W for the ITO anode device. |
