Charge injection in polymer light-emitting diodes

The injection-limited hole current from Ag into poly-dialkoxy-p-phenylene vinylene (PPV) exhibits a weak dependence on temperature, in spite of the presence of a large injection barrier of 1 eV. The measured field- and temperature dependence of the hole injection is explained by a hopping model in which energetic disorder is taken into account. In a PPV-based light-emitting diode it is demonstrated that the hole injection is enhanced by the presence of electrons. As a mechanism for this enhanced hole injection an increase of the electric field at the hole injecting contact due to trapped electrons is proposed.