Determination of trapping parameters in poly(p-phenylenevinylene) light-emitting devices using thermally stimulated currents

Employing thermally stimulated current (TSC) technique, the existence of distinct trap distributions in poly(p-phenylenevinylene) (PPV) light-emitting devices has been established. In devices with an indium tin-oxide (ITO) anode two TSC peaks in the temperature range between 100 and 150 K are observed. They correspond to trap levels with a depth of 0.03–0.06 eV and 0.13–0.18 eV, respectively. The total density of these trap species is of the order of 1016 cm−3 which is in good agreement with the dopant concentration obtained from capacitance-voltage measurements. The investigated peaks in the TSC spectrum do not occur if a Au electrode is used instead of ITO. Hence, the reaction of ITO with the elimination products (mainly HCl) during the conversion of the PPV precursor leads to the formation of these shallow traps. Deeper trap states with energies between 0.6 and 1 eV have been detected, too. The latter trapping levels appear independently of the anode substrate material and are due to the influence of air.