The increase of operational lifetime for Organic Light-Emitting Diodes has stimulated many studies focused on the mechanisms responsible for their degradation. Degradation studies of the N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine thin films have been performed using synchrotron radiation in order to elucidate the modification of the electronic structure in such organic compound, when non-monochromatized light was used to simulate the degradation caused by intense sunlight. Core level photoabsorption at the N 1s-edge and valence level photoemission measurements suggest stronger structural stability and a minor loss in the hole transporting properties. The degradation leads to the decrease of the injection and charge mobility, associated with the loss of nitrogen and benzene rings, which causes an increase of the impedance in the electroluminescent device. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.