Effects of UV radiation on the charge trapping capability of PET

TL;DR

This study investigates how UV radiation exposure enhances the charge trapping ability of PET by creating new, shallower traps, affecting its electrical properties over time.

Contribution

It provides detailed characterization of UV-induced trap formation in PET, including trap depth distribution and relaxation kinetics, using PEA and TSDC techniques.

Findings

UV irradiation increases charge retention in PET.

New traps are shallower and more widely distributed.

Charge relaxation times become more dispersed with exposure.

Abstract

Poly(ethylene terephthalate) (PET), as most dielectric materials, is able to retain space charge in traps. This allows the material to attain an almost-permanent polarization when space charge is displaced by an external electric field or it is injected from an electrode. We have studied the influence of UV irradiation on the charge trapping capability of PET in samples exposed for different periods of time, up to 10 weeks. The pulsed electro-acoustic technique (PEA) has been used to determine the charge profile. The injected charge that the material is able to retain on the irradiated surface increases with irradiation time. This indicates the formation of new traps. An extensive characterization of these localized states has been performed by thermally stimulated depolarization currents (TSDC) technique. Parameters of charge relaxation kinetics have been obtained fitting spectra of the $\rho_c$ peak, related to injected charge, to the general order kinetics model. A relaxation map analysis shows that relaxation times become more distributed and the activation energy decreases as irradiation time is increased. The activation energy decreases approximately by 10% after 10 weeks of exposition. These results show that UV irradiation creates additional traps on the treated surface, which agrees with PEA results, and that these traps are shallower and their energy depth distribution is wider than in the case of pre-existing traps.