Metal contact effect on the persistent internal polarization in pure and doped polystyrene

Photo-electrets of pure and copperphthalocyanine doped polystrrene films (thickness 20 μm) were formed by UV- radiation in an electric field with Al, Cu, Ni, Zn, Cd and Pb as electrode materials. The depolarization current and the released charge show a strong dependence on the material of the electrode. Two distinct regions in the current decay characteristic indicate that the polarization consists of trapped holes and electrons. The amount of charge injected increases with decreasing work function of the contact metal. Doping increases the stability of the charge.