Correlation between dark spot growth and pinhole size in organic light-emitting diodes

Our in situ experimental observations of dark spot growth in organic light- emitting diodes using optical microscopy show a linear rate of growth for t he area of all the dark spots. We used uniformly sized silica micro particl es to intentionally create size-controllable pinholes on the cathode protec tive layer. Subsequently, we observed initial formation of dark spots as a result of these pinholes and then monitored their growth. Due to usage of p articles of various diameters, we were able to linearly correlate the growt h rate with pinhole size. This allows us to estimate the original pinhole s izes that gave rise to the dark spots, which we believe were initiated by " dust" particles. Our studies verify that dark spot formation is due to pinh oles on the protective layer that creates pathways for water or oxygen perm eation, and that dark spot growth is dependent on the pinhole sizes. (C) 20 01 American Institute of Physics.