Inhibition of dark spots growth in organic electroluminescent devices

Humidity-induced oxidation has been considered as a major cause for the gro wth of dark spots in organic electroluminescent devices. In this Letter, we found that a layer of 100 nn thick calcium deposited on top of the magnesi um:silver (Mg:Ag) cathode can slow down the growth rate of dark spots. Furt her experiments verified that calcium not in direct contact with the cathod e could not protect the dark spots against growing. This excludes the possi bility that the protective function of calcium derives solely from its acti on as a moisture-resistive agent. In contrast, calcium functions as a sacri ficial metal forming a galvanic couple with the magnesium electrode such th at calcium would oxidize in preference to the Mg:Ag. (C) 2001 Elsevier Scie nce B.V. All rights reserved.