Photoconductivity in ultrathin oligo(phenylene vinylene) films during vapor deposition

The photoconductivity (PC) of oligo(phenylene vinylene) (OPV) films during vapor deposition was measured as a function of the chain length of the OPV molecules. The films show PC even in sub nanometer thicknesses immediately after deposition. With short OPVs, the PC vanishes completely within 10 minutes, whereas with longer OPVs, the PC signal keeps rising after deposition. By comparison with optical absorption, luminescence and light scattering experiments, we show that the effects can be ascribed to a transformation from amorphous films to aggregates and microcrystallites.