Current Injection from a Metal into a Disordered Hopping System. III. Comparison between Experiment and Monte Carlo Simulation

We have performed electric-field and temperature-dependent electron injection studies in an aluminum/tris(8-hydroxy-quinolinolato)aluminum/ magnesium:silver single-layer organic light-emitting diode. Analysis of the observed injection currents in terms of the classic Fowler--Nordheim (FN) tunneling or Richardson--Schottky (RS) thermionic emission proved to be inadequate. Whereas the FN-type behavior at high electric fields must be considered accidental, the injection currents qualitatively resemble those of the RS concept. However, quantitative differences are observed concerning the RS coefficient, the prefactor current, and the temperature dependence. On the other hand the experimental data are in excellent agreement with a recently presented Monte Carlo simulation
[U. Wolf et al., Phys. Rev. B 59, 7505 (1999)] of carrier injection from a metal into an organic dielectric with random hopping sites.