Microcavity organic light-emitting diodes on silicon

We study resonant-cavity organic light-emitting diodes made on silicon substrates. The device structure is Al/indium–tin–oxide (ITO)/copper phthalocyanine (CuPc)/a triphenylamine derivative (TPD)/tris-(8-hydroxyquinoline) aluminum (Alq3)/cathode, where the cathode is a semitransparent Al layer or a LiF/Al stack. We use a model based on the transfer-matrix method to deduce the wavelength dependence of the ITO refractive index, and to calculate the spectra and the angular emission diagrams of the diodes. Microcavities limit the spectral and spatial distributions of the emitted light in accordance with the model. Current–voltage characteristics of various devices prove that a thin LiF layer improves the injection of electrons in Alq3 from semitransparent aluminum cathodes.