Ionization-assisted deposition of 8-hydroxyquinoline aluminum for organic light emitting diode

Ionization-assisted deposition (IAD) was applied for the preparation of 8-hydroxyquinoline aluminum (Alq) in the fabrication of organic light-emitting diodes (LEDs) in the structure of indium-tin-oxide glass/spin-coated polyvinylcarbazole (PVCz)/Alq/vacuum-deposited Mg. When Alq was deposited by IAD directly on PVCz, the luminance at a low drive voltage increased with increasing ion acceleration voltage up to 150 V. However, high ion acceleration caused a leakage current that does not contribute to luminescence, due probably to radiation damage in the PVCz/Alq junction. To avoid ion irradiation at the interface, Alq was deposited in two steps, in which the ion acceleration voltage was turned off in the first stage of deposition. The device characteristic was improved with the addition of this buffer layer. When the first two-thirds of the Alq layer was deposited without ion acceleration, luminescence efficiency was two fold higher than that in the case of no-acceleration deposition or vacuum deposition. The Alq layer formed by IAD had higher surface smoothness, which would contribute to the improvement of the Alq/Mg junction.