EFFECT OF IMPURITY IONS AND PERMANENT DIPOLES FOR DEVICE PERFORMANCE OF THIN-FILM ELECTROLUMINESCENT DIODES

摘要

Double-layer EL diodes composed of a spin-coated Polyvinylcarbazole (PVCz) layer and a vacuum-sublimed tris-(8-hydroxyquinoline)aluminum (Alq) layer were prepared. The diodes with the same device structure but with PVCz layer with added ionic impurities were also prepared. The diodes were driven at constant voltage and allowed to stand under short-circuit or reverse bias conditions. Observations of luminance-current density-voltage relations at constant voltage driving were repeated. The decrease of both luminance and current density during constant voltage driving were observed. Both spontaneous and reverse-bias assisted recovery of device performances were observed and these degradation and recovery phenomena were discussed in terms of the movement of ionic impurities in organic layers.