Scientists from the Institute of Materials Research and Engineering in Singapore have examined the formation of dark spots in organic LEDs caused by dome-shaped bubbles at the interface between an emissive and nonemissive diode layer.Using the combination of a Nikon E600 light microscope, a time-of-flight secondary ion mass spectrometry instrument and a Jeol JSM-6700F scanning electron microscope, they observed that the bubbles are the result of electrode roughness, local current concentration and heating that leads to material degradation. In a description published in the Jan.14 issue of Applied Physics Letters, the researchers suggest that stabilizing and smoothing the interface can reduce formation of such dark spots.