UV photocurrent spectroscopy in poly(p-phenylene vinylene) and derivatives

We present photocurrent measurements of poly(p-phenylene vinylene) (PPV) and derivatives for photon energies up to 5.0 eV. We observe photocurrent peaks related to the first, second and third absorption peaks, which we associate with the dissociation of a succession of increasingly energetic excitons. We have performed INDO/SCI calculations for the five-ring PPV oligomer, which show different distributions of the electronic charge of the exciton wavefunction over the chain at different excitation energies. We discuss the significance of these states for the photoconduction in PPV and question the applicability of a band-based model.