Influence of carrier-injection efficiency on modulation rate of organic light source.

We have investigated the relationship between the energy levels of an emissive layer and the modulation rate of organic light-emitting diodes (OLEDs) based on a distyrylbenzene derivative, 1,4-bis[2-[4-[N,N-di(p-tolyl)amino]phenyl]vinyl]benzene (DSB). By utilizing DSB as an emitting material, a high modulation rate can be realized because of the short fluorescence lifetime of 0.2 ns of DSB. Furthermore, we also found that an energy gap between an emissive layer and an adjacent organic layer is an important parameter to improve modulation rate. DSB-doped 4,4-bis(2,2-ditolylvinyl)biphenyl is the best combination of all the organic materials used in this study, and the fastest cutoff frequency of 10 MHz has been achieved for the OLED in spite of the large emitting area of 1 mm(2).