EVIDENCE FOR THE FORMATION OF UNOCCUPIED STATES IN POLY(2,3-DIPHENYLPHENYLENE VINYLENE) FOLLOWING THE DEPOSITION OF METAL

Near-edge x-ray-absorption spectroscopy was used to study the interact ion of Ca and Al with poly(2,3-diphenylphenylene vinylene) (DP-PPV). A l does not significantly modify the C-K edge during interface formatio n while Ca does in a coverage dependent fashion. The evolution of the C-K edge points to the creation of new intragap states. In addition, w e see a strong resonance at higher photon energies. The creation of ne w unoccupied states in DP-PPV following the deposition of Ca may in pa rt explain the enhanced charge injection observed when Ca is used as t he cathode material in polymer-based light emitting diodes.