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/Alq(3) multiple quantum-well (MQW) structures are investigated in detail. The threshold duty-ratio (delta(th)) is found in the NPB/Alq(3) MQW devices, whereas the bilayer NPB/Alq(3) device does not appear. Then the delta(th) 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 delta(th), while the double QW device is the opposite. This is due to the charge diffusion effect in the Alq(3) 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.