Analysis of dark spots growing in organic EL devices by time-of-flight secondary ion mass spectrometry

Chemical structural analysis of tape-stripped surfaces at dark spots growin g in organic electroluminescent (EL) devices during exposure to the atmosph ere was done by time-of-flight secondary ion mass spectrometry (TOF-SIMS), The EL devices consist of indium-tin-oxide, triphenylamine -tetramer, tris( 8 -hydroxyquinoline)aluminum (Alq(3)), and a Mg-Ag cathode deposited in ord er under vacuum on a glass substrate. It was found that the interface betwe en the Alq(3) layer and the Mg-Ag cathode was exposed as a result of tape-s tripping, where a large number of dark spots were observed on both sides. S econdary ion images of O-, Mg+, and Alq(2)(+) were observed from the dark s pots on the cathode side. On the other hand, Mg+ and O- images with a nucle us in the center were observed from the Alq(3) side. It is concluded from t he results that the constituent element Mg of the cathode was oxidized at t he interface adjacent to the Alq(3) layer during exposure to the atmosphere , forming a dark spot with a nucleus in the center. Finally, it was confirm ed that the TOF-SIMS analysis of the tape-stripped surface is useful for th e analysis of the mechanism of dark spot formation.