Dependence of the hole-injection barrier on the hole conductor in organic light emitting diodes based on composites

Organic light-emitting diodes based on composites using different hole conductors were fabricated and characterized. In these devices the current flux is limited by the injection of holes into the semi-conducting polymer layer through tunneling. The data were evaluated using the common Fowler-Nordheim formalism. The barrier height was found to depend linearly on the oxidation potential of the hole conductor, but unexpectedly the slope is only 0.55±0.1. This result is explained by the non-polar nature of the internal interface between ITO and the conductive layer.