Measurement setup to simultaneously explore the location and energy of trapped charges in thin polymer films

Abstract

This research proposes a unique system that combines charge density measurements by the laser intensity modulation method with optically excited current acquisitions using the photo-stimulated discharge technique (PSD). The purpose of this setup is to investigate the relationship between space charge properties (such as density, spatial depth, and time evolution) and the photocurrent-associated energies in order to gain new insights into the trap population and detrapping mechanisms in thin polymer films. This paper presents a description of the technical principles of both methods as well as the whole combined system. The results on a 12 μm-thick polyethylene naphthalate film show pyroelectric currents, which after processing indicate the formation of homocharges whose magnitude and depth decrease after light irradiation. The PSD currents allow the identification of two major energy bands at 3.4 and 5.9 eV (360 and 207 nm, respectively), possibly related to charge detrapping. In addition, current transients during constant wavelength irradiation show that incident photons can interact differently with trapped charges depending on the applied field.