The role of MgF2 buffer layer in tris-(8-hydroxyquinoline)aluminium-based organic light-emitting devices with MgAg cathode

摘要

The device characteristics of organic light-emitting devices based on tris-(8-hydroxyqunoline) aluminium with a thin layer of MgF2 inserted at the indium-tin-oxide (ITO) and organic interface or the organic and Mg:Ag cathode interface are investigated. A 1.0 nm MgF2 thin layer can enhance electron injection when it is inserted only between organic electron transporting layer and Mg:Ag alloy cathode, but can block hole injection when it is inserted only between the ITO anode and organic hole transporting layer. By inserting MgF2 at both sides on the ITO anode and under the Mg:Ag cathode, the current efficiency of the device is improved by 74%, and power efficiency is also improved by 18% at a current injection of 20 mA cm(-2), compared to the standard device without MgF2 buffer layer. This is due to the increased electron and decreased hole injection, which results in more balanced electron and hole injection, and more efficient exciton formation. The increased electron injection can be well understood by the tunnelling effect model.