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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.

We have used polyvinylcarbazole, PVK, in combination with poly( p -phenylenevinylene). PPV and a green-emitting, soluble derivative, poly(4,4′-diphenylene diphenylvinylene), PDPV, to fabricate triple-layer light-emitting diodes ITO/PPV/PVK/DPV/Metal. We report luminances in excess of 1300 cd/m with Al cathodes, turn-on voltages of ∼8V in structures 300 nm thick, and internal efficiencies in the range 0.4-0.8% for Al and Ca cathodes; at least 10 times higher than for single-layer PDPV devices. In addition, the efficiencies for Ca or Al electrodes are only a factor 1.5 different. The improvements over single-layer PDPV devices are interpreted as due to better hole-injection by PPV and to the formation of a hole-barrier at the PPV/PVK interface, which forces a better balance of the electron- and hole-currents.