The occurrence and formation of black spots areas in PolyLED devices has been studied by time-of-flight SIMS (TOFSIMS). The composition, shape and position of the black spots is visualised by three-dimensional (3D)-TOFSIMS depth-profiling. It has been established that the formation of non-emissive spots is due to the growth of aluminium, oxide clusters at the AIBa/polymer interface. Electron injection in the black spots is lost by the resulting local increase of the resistivity of the cathode. (c) 2006 Published by Elsevier B.V.