Enhancing the electron injection in polymer light-emitting diodes using a sodium stearate/aluminum bilayer cathode

In this contribution the molecule sodium stearate (NaSt) is used for the first time as electron injection layer in combination with the fluorescent polymer phenylene substituted poly (para-phenylenevinylene) (Ph-PPV) in organic light-emitting diodes (OLEDs). The fabricated devices show current efficiencies up to 8.4 cd/A, indicating that the employed NaSt/aluminum (Al) bilayer cathode has adequate electron injection capabilities in conjunction with Ph-PPV and, therefore, NaSt has the potential to become a non-toxic alternative to the widely-used alkali halide lithium fluoride (LiF).Numerical simulations of the device structure are performed which are in good agreement with the experiments. Additionally, it is shown that the NaSt/Al cathode of the presented device cannot be simply modeled by using a low work function contact, as it is commonly done for the LiF/Al cathode in simulations of multilayer devices. Instead, an alternative approach is introduced in which an insulator in combination with the Fowler–Nordheim tunneling and the direct tunneling model is chosen to describe the charge carrier injection through the NaSt layer.

Figure optionsDownload as PowerPoint slideHighlights
► Polymer light-emitting diodes are fabricated using a sodium stearate/aluminum bilayer cathode.
► Current efficiencies up to 8.4 cd/A are obtained.
► Numerical simulations of the device structure are in good agreement with the measurements.
► Fowler–Nordheim and direct tunneling models are used to describe the injection properties of the bilayer cathode.