Anisotropy of Photoconduction in Polyimide

An anisotropy of photoconduction in polyimide was investigated in relation to the molecular orientation. The anisotropy of the molecular chain alignment was observed by wideangle X-ray diffraction. The photocurrents in the three directions were measured. The in-plane photocurrents were anisotropic. As polyimide was drawn, the molecular chain had a tendency to arrange along the drawing direction and the inplane photocurrent in the normal to the drawing direction was larger than that in the parallel direction. As the degree of intermolecular order increased, the photocurrent normal to the film plane decreased, but the in-plane photocurrent increased. Polarized infrared measurements showed that the plane of monomer rings tended to rotate toward the direction perpendicular to the film surface by drawing. It was concluded that the anisotropy of the photocurrent is caused by the alignment and orientation of molecular chains, and carriers move readily along the stacking direction of phenyl and imide rings.