Improved stability of organic light-emitting diode with aluminum cathodes prepared by ion beam assisted deposition

We have fabricated highly stable organic electroluminescent devices based on spin-coated poly-p-phenylene-vynylene (PPV) thin films. The electrical properties of aluminum cathode, prepared by ion beam assisted deposition, on PPV have been investigated and compared to those by thermal evaporation. Although energetic particles of Al assisted by Ar⁺ ion may damage the organic material, I-V-L characteristics are improved by applying thin Al buffer layer. In addition, a dense Al cathode inhibits the permeation of H₂O and O₂ into PPV film through pinhole defects, and thus retards dark spot growth. It may be deduced from highly packed structure of Al cathode with an increase in the contact area between Al and PPV that reduce the contact resistance. In conclusion, the lifetime of organic light-emitting device (OLED) has been extended effectively by dense Al film through ion beam assisted deposition process.