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
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