Longevity of organic light-emitting devices with aluminum cathodes prepared by ion beam assisted deposition process

Highly stable organic electroluminescent devices based on spin-coated soluble phenyl-substituted poly-p-phenylene-vinylene (Ph-PPVs) thin films have been achieved. We investigated the electrical properties of ion beam assisted aluminum cathode contacting Ph-PPV and compared them to those of thermal evaporation. Although energetic particles of Al assisted by Ar+ ion generate the damages in organic materials, I–V–L characteristics can be improved by using thin Al buffer layer to avoid damages. In addition, dense Al cathode inhibits the permeation of H2O and O2 through pinhole defects, which results in retarding gas bubble formation. This may be explained by highly packed structure of Al cathode and decrease of the contact resistance between Al and Ph-PPV. It is believed that the larger contact area and increase of density of state in Ph-PPV minimize the contact resistance and that results in the longevity of organic light-emitting devices (OLEDs).