Organic Light-Emitting Diodes Using Polyaniline Nanofilm as a Hole-Injection Layer

Polyaniline nanofilms were applied to the hole-injection layer of organic light-emitting diodes. The polyaniline nanofilms were prepared by Langmuir-Blodgett deposition of polyaniline/dodecylbenzenesulfuric acid ion-complex monolayer on a water surface onto ITO anodes. Introduction of the polyaniline nanofilms to organic light-emitting diodes causes the onset voltage for the emission to reduce from 7.0 V to 6.0 V and the injection current and the luminescence to increase by one order of magnitude. The results demonstrate the polyaniline nanofilms have the hole-injection ability. Moreover, the hole-injection and luminescent properties for the pernigraniline-form of fully oxidized polyaniline were better than those of the emeraldine salt partially oxidized polyaniline, but current and power efficiencies were worse because of the lack of carrier injection balance. Compared with the spin-coated films, the existence of the polyaniline films is important to reduce the onset voltage, but it does not depend on the film thickness.