Thermally stimulated depolarization current studies in thin films of sulfonated polystyrene ionomers

Ionomers are charged polymers that exhibit singular electrical properties, which can be applied at different technological branches. More recently they have been applied as transport layers at PLEDs (Polymer Light-Emitting Diodes) devices. In particular, thin films of ionomer have been deposited between the cathode and the luminescent active layer, improving the efficiency of the charge injection [1, 2]. Despite the success of such applications, the involved phenomena related to charge storage and transport mechanisms in ionomer thin films are still challenge to be elucidated. A detailed study of thermally stimulated depolarization current (TSDC) was carried out to investigate dipolar relaxation and the charge storage phenomenon in films of sulfonated polystyrene (SPS) ionomers having lithium as counterions. TSDC of SPS thick samples (80 μm), polarized at temperatures higher than the glass transition temperature, showed three peaks: one at lower temperature (peak ß), an intermediate peak (peak α), and a third that appeared at a temperature coincident with the polarization temperature (peak ρ). Quantitative information about trapping-detrapping and dipolar relaxation and their corresponding activation energies was determined by fittings of the deconvoluted peaks with kinetic relaxation processes. In very thin films, below 50 nm, the peak ß is not recorded, and the dependence of peaks α and ρ on the polarization temperature and on the polarization field are different from those observed for thick films.