Improved Electron Injection in Organic Light Emitting Devices by Applying Thin Insulating Layers

Abstract

We present the fabrication and characterization of organic light emitting devices (OLEDs) using thin insulating layers for improved electron injection. The OLEDs are constructed with an ITO anode and an aluminum cathode. For the active layer we use either ladder-type Polyparaphenylene (m-LPPP) or Parahexaphenyl (PHP). A thin film of an insulating material is applied between the active layer and the cathode, in order to achieve a better tunnel injection due to a higher electric field at the interface. We compared different insulating materials with various thickness. The best results are obtained by using a LiF-layer with a thickness between 10 Å and 15 Å. Thereby the onset voltage decreases and the current density in the device increases significantly.