A long-lived organic light emitting diode (OLED) was fabricated using a dense aluminum cathode prepared by the ion-beam-assisted deposition (IBAD) process. We investigated the passivation properties of ion-beam-assisted and thermal evaporation-induced aluminum cathodes mounted on Ph-PPV. The dense and highly packed At cathode effectively prevents the permeation of H2O and O-2 through pinhole defects, which results in retarding dark spot growth. Employing thin Al buffer layer diminished Ar+ ion-induced damages in Ph-PPV and limited permeation against H2O and O-2. The interface between Al and Ph-PPV may be modified in IBAD case, even though buffered Al layer was deposited to 30 nm by thermal evaporation prior to Ar+ ion beam irradiation. It is believed that the buffered Al film cannot screen the Ar+ ions or Al atoms wholly due to the existence of pinholes or non-deposited regions among the columnar structures. (C) 2004 Elsevier B.V. All rights reserved.