Electrical properties of iodine-doped nickel (phthalocyanine) films

The change in electrical conductivity of a vacuum evaporated nickel phthalocyanine (Ni(Pc)) film with doping of iodine has been studied based upon the analyses of the film structure, electronic spectroscopy, and electron spin resonance measurements. It was found that an abrupt increment of electrical conductivity at the first stage of incremental doping is accompanied by a phase transition from a monoclinic system to a tetragonal system. This phase transition causes cracks on the surface of film and leads to the collapse of the polycrystalline structure upon further doping. It is concluded that a gentle increase in the electrical conductivity with further doping is limited by the competitive process between the increment of charge carriers and the decrement of the electrical conduction path, and a collapse of the polycrystalline structure due to a phase transition.