Degradation of organic light-emitting devices due to formation and growth of dark spots

We present our in-situ experimental observations of dark spot growth in OLED devices using optical microscopy. In order to understand the formation mechanism of dark spots, we employed silica particle to intentionally create some predictable pinhole defects on the protective layer. We found a linear growth of all dark spot as well as a linear correlation between growth rate and area. These results indicate that dark spot formation is related to corrosion of the calcium or other materials with water and oxygen through pinhole defects. Furthermore, we found a correlation between the degradation of entire devices and growth of all dark spots, which allows us to predict the lifetime of entire devices.