Abstract
With the development of organic light-emitting diodes, interests in the mechanisms of charge carrier photo generation, separation, transport and recombination continue to grow. Phosphorescent organic light-emitting diodes have gained considerable interest in the last 10 years because of high luminance efficiency. In the present paper, the authors investigated the optical and electrical characteristics of the devices based on Ir(ppy)3 and Ir(piq)3 doped PVK matrix emission layer at room temperature. The PL spectra show that the energy transfer from PVK to Ir(piq)3 is harder than that of PVK to Ir(ppy)3. The Luminescence characteristics of devices with different doping ratio show that it is not the energy transfer from matrix, but the recombination of injected carriers on phosphorescent molecules that is the main origin of EL emissions. From the viewpoint of energy level, the characteristics of carrier-trap and transport in Ir(piq)3 are better than in Ir(ppy)3 due to the high HOMO and low LUMO in Ir(piq)3.