Thermally stimulated processes in heterocyclic materials suitable for heterolayer organic light emitting diodes

Abstract We studied ultraviolet photoelectron spectroscopy (UPS) and thermally stimulated processes in two types of phenylquinoxalines, and one type of starburst trisphenylquinoxaline in order to characterize the valence band structure and the localized states. An ionization potential of about 6.0 eV was determined for each material using UPS. Thermally stimulated discharge currents (TSDC) gave evidence of dipolar and/or charge transport mechanisms. We assigned each TSDC peak to the different elementary processes using in addition dielectric spectroscopy (DES), and from thermally stimulated luminescence (TSL) curves, performed for the first time on these materials, we estimated the mean trap depths.