Dynamic turn-on behavior of organic light-emitting devices with different work function cathode metals under fast pulse excitation

We investigate the electroluminescence (EL) response of organic light-emitting diodes (OLEDs) with different metal cathodes and device-area dependence. Moreover, we formulate the EL delay time, which is an indicator of the EL response. The EL response is fundamentally governed by the device area, i.e., the capacitance of the device, and this for the OLEDs with low work function metals as a cathode is fast. According to the formulation, we estimate electron mobility in an organic bilayer and the threshold electric fields for electron injection under fast-pulse excitation. It is consequently demonstrated that electron mobility in the bilayer showed mixed mobility characteristics for each layer, and the threshold electric field became smaller with a decrease in the work function of cathode metals. The low work function metal cathode device is identified as a high-speed EL response device. (C) 2003 American Institute of Physics.