Current-induced fluorescence quenching in organic light-emitting diodes

The electroluminescence quantum efficiency of organic light-emitting diodes with a doped Alq [tris(8-quinolinolato)aluminum] emitting layer is found to decrease markedly with increasing current density. This phenomenon was investigated using multilayer device structures permitting bipolar or unipolar carrier transport, and luminescence measurements with simultaneous optical and electrical excitation. The loss of electroluminescence quantum efficiency is attributed to the quenching of the singlet-excited state of the dopant by a cationic species. (C) 2002 American Institute of Physics.