Photogeneration in an acceptor-type poly(phenylenevinylene)

Stationary photoconduction in thin films of a cyano-phenylamine-substituted poly-phenylenevinylene, in both sandwich and gap arrangement, has been studied. In order to separate electrode from bulk effects a thin layer of SiOx could be inserted between the indium-tinoxide (ITO) electrode and the film. Photocurrents were measured as a function of electric field, temperature (100 to 300K), photon energy (2.5 to 5 eV) and polarity of the applied bias. The results indicate that for h upsilon P < 3.2 eV the photocurrent is a superposition of bulk ionization involving relaxed singlet excitons and, depending on the direction of the electric field, exciton induced injection of predominantly electrons from the ITO. For h<upsilon> > 3.2 eV intrinsic photogeneration from hot singlet excitons takes over.