Formation and growth of black spots in organic light-emitting diodes

Abstract

We report electroluminescence (EL) degradation studies of thin-film organic light-emitting diodes under ambient conditions. Bilayer organic ITO/TPD/Alq3/Mg/Ag devices were studied via EL and photoluminescence (PL) microscopy. In situ imaging of device luminescing areas and measurement of sample luminance were performed, allowing for a detailed study of black spot formation and luminance reduction under constant voltage stress conditions. Post-stress devices were further characterized using PL microscopy, and it was found that black spots result from delamination of the metal at the Alq3/Mg interface initiated by pinholes on the cathode, caused by substrate defects.