Intrinsic and extrinsic charge carrier photogeneration in phenyl-substituted polyphenylenevinylene-trinitrofluorenone blend systems

Spectral, field, and temperature dependencies of steady-state photoconductivity were studied in thin films of pure phenyl substituted copolymeric polyphenylenevinylene (PhPPV) and PhPPV doped by trinitrofluorenone. The films were sandwiched between indium tin oxide (ITO) and aluminum as well as between two aluminum contacts. Typical surface extrinsic carrier photogeneration was observed in ITO/PhPPV/Al samples with positively biased ITO while the intrinsic photoconductivity dominated in Al/PhPPV/Al samples and ITO/PhPPV/Al sandwiches with negatively biased ITO. Charge carrier photogeneration in both doped and undoped PhPPV at higher photon excess energies was found to be in good agreement with predictions of the hot exciton dissociation model. At low excess photon energy of the inducing light, carrier photogeneration is ascribed to dissociation of optical excitations on charge transfer centers which are either dopant molecules in the doped samples or intrinsic defects in the pure material.