Formation of dark spots induced by crystallization of organic layers in organic light-emitting diodes

Abstract

We report electroluminescence degradation in organic light emitting diode as a function of applying bias. A number of dark spots were produced as applying bias increased. Microscope image showed that dark spots are related to many protrusions and hollows formed on Al electrode. X-ray diffraction and x-ray micro-diffraction indicate that Joule heat from high electric field induced the crystallization of organic materials, forming dark spots via peeling-off the Al cathode from Alq3 layers.