Effect of photoemission from electrode on photo-stimulated discharge spectra

Photo-stimulated discharge (PSD) method is a direct and powerful method to obtain the charge trap depths in polymeric materials. However, PSD spectra are induced not only by the de-trapping space charges in the film but also by the photoemission from electrodes or polymer. Therefore, the study on the photoemission mechanisms in PSD measurement is of great significance for correctly interpreting the PSD spectra. In this study, monochromatic light irradiates the polypropylene film which is covered by deposited finger or solid electrodes (Au or Al). The measurements are carried out when the sample is under different DC voltages. It is found that, when the sample has solid Au electrodes on its both sides, the photocurrent peak positioned at 320 nm is due to the photo-stimulated de-trapping charges in polypropylene and that the peak positioned at 270 nm generates not only from photo-stimulated de-trapping charges but also partially from photoemission from electrode when solid Au electrodes are used.