Electrical Conduction and Luminescence for Inverted-Type Organic Light-Emitting Diodes with Polyethyleneimine

Abstract

Organic light-emitting diodes (OLEDs) have showed the unique potentials of display by bendable, foldable and storable panels. In general, since OLEDs consisted of multi organic layers, their electrical conduction would be complicated. Aluminum quinoline (Alq3) was a classical and famous fluorescent material. We studied the conduction properties of inverted Alq3-bilayer OLEDs. Since the barrier height of electron injection from ITO cathode to Alq3 was higher than that from LiF/Al, electrons were little injected into Alq3 and the current density in the absence of EL was controlled by holes. In the specimen using polyethyleneimine as an injection layer, the current density and hole injection were influenced by electron injection for the current continuity. Despite that holes could arrive at the counter cathode through Alq3, the recombination zone was located near a hole transport layer as the conventional bilayer OLED. It was suggested that the carrier transport in an organic layer depends on both carrier injections.