INTERFERENCE PHENOMENON DETERMINES THE COLOR IN AN ORGANIC LIGHT-EMITTING DIODE

We report on electroluminescence from two-layer organic diodes made of poly(3-methyl-4-octylthiophene) and iphenylyl)-5-(4-tert-butylphenyl) -1,2,4-oxadiazole films between electrodes of indium tin oxide and Ca/ Al. The diodes emitted light in the green-blue range; the electrolumin escence spectra varied between diodes with different thicknesses of th e polymer and molecular layers. The optical phenomena were simulated w ith a model accounting for interference effects; simulated results sho wed that the electroluminescence from the organic diode can be due nei ther to luminescence of the polymer nor of the molecular layer. These model simulations, together with electrochemical measurements, can be interpreted as evidence for an indirect optical transition at the poly mer/molecule interface that only occurs in a strong electric field. We label this transition an electroplex. (C) 1997 American Institute of Physics.