Improved electron injection into Alq3 based devices using a thin Erq3 injection layer

The role of a thin erbium(III) tris(8-hydroxyquinoline) (Erq3) interface layer on the electron injection into aluminium(III) tris(8-hydroxyquinoline) (Alq3) based organic light emitting devices (OLEDs) has been investigated. It has been shown that the use of a 40 A interface layer can increase the efficiency of a simple Alq3 OLED with an Al cathode to a level comparable with other, well established, high-efficiency cathodes such as LiF/Al. We also show that, despite the bulk HOMO and LUMO positions for Erq3 being little different from those for Alq3, the presence of an interfacial layer makes the devices turn-on voltage almost independent of the cathode metal. This is explained by there being a vacuum level shift for Erq3 which is dependent on the work function of the cathode metal.