Electron injection and transport in 8-hydroxyquinoline aluminum

We have measured the current-voltage characteristics and device efficiency of organic Light emitting diodes (OLEDs) based on 8-hydroxyquinoline alumin um (Alq(3)) in combination with several cathode layer setups. The electron injection properties of cathode metals evaporated under high vacuum (HV) an d ultra-high vacuum (UHV) conditions are compared. Further, cathodes incorp orating a thin layer of lithium fluoride, which is covered with a metal cap ping layer, are investigated. It will be shown that aluminum is an outstand ing capping metal and significantly improves both electron injection and de vice efficiency. Quasi-static and transient current-voltage measurements on single-layer devices will be presented. It will be demonstrated that catho des, comprising 0.2 nm LiF and aluminum, are able to sustain space charge l imited currents in Alq(3). Additionally, the efficiency and lifetime data o f multi-layer devices using this cathode layer setup are discussed. (C) 200 0 Elsevier Science S.A. All rights reserved.