Effect of stretching on the structure and electrical conductivity of doped and undoped poly(phenylene vinylene) thin films

Impedance spectroscopy, X-ray diffraction, infrared dichroism and AFM imaging were used to investigate the effect of orientation and doping on the electrical properties of a series of stretched poly(phenylene vinylene) (PPV) films. The degree of orientation was determined by infrared dichroism. X-ray diffraction patterns clearly display a transition from random orientation to a high degree of orientation. Analysis of the AFM images indicates that a fibrillated structure was formed on the stretched films. Solid state impedance measurements of doped and undoped films were carried out parallel to and perpendicular to the stretch direction (i.e. in the through-plane direction) in an attempt to understand the effect of the fibrillar structure on the electrical properties. It was found that the bulk conductivity of undoped PPV in the through film thickness direction decreased with increasing orientation, while the conductivity of undoped PPV along the stretch direction is independent of orientation. Doping of the stretched PPV thin films with a 0.58 M FeCl3 solution for 10 min increased the conductivity by over two orders of magnitude.