The charge confinement effect of quantum-well Alq3-based OLEDs by dual-pulsed transient electroluminescence

In this paper, the dual-pulsed transient electroluminescence (EL) characteristics in organic light-emitting diodes (OLEDs) with NPB/Alq3 multiple quantum-well (MQW) structures are investigated in detail. The threshold duty-ratio ( δth) is found in the NPB/Alq3 MQW devices, whereas the bilayer NPB/Alq3 device does not appear. Then the δth in single and double wells are 0.68 and 0.35, respectively. In the single QW device, the second pulsed intensity will be greater than the first pulsed strength after reaching the δth, while the double QW device is the opposite. This is due to the charge diffusion effect in the Alq3 well layer near the cathode of MQW devices. As the well numbers increase, it is different from the fall time remaining almost constant, the transient delay time will increase linearly, which is totally caused by the recombination position of excitons.