In this paper, the electrical and optical properties of organic light emitting diodes (OLEDs) are analyzed, deriving the devices limits at high applied electric fields. In particular, for different device thicknesses, it is possible to conclude that the optical breakdown can be attributed to a surface phenomenon, that the temperature of electrical failure is significantly different from the optical one, that the two phenomena of failure are markedly similar at different thicknesses and that there is a maximum field beyond which the thin cathode may be destroyed due to phenomena not agreeable to thermal events. © 2012 American Institute of Physics.