Using ZnS Nanostructured Thin Films to Enhance Light Extraction from Organic Light-Emitting Diodes

Abstract

Wide band gap semi-conductor zinc sulfide (ZnS) nanocolumn arrays were prepared on the glass side of indium tin oxide (ITO) substrates by glancing angle deposition (GLAD) technology. The scanning electron microscopy (SEM) images show the formation of ZnS nanocolumn arrays when the glancing angle was set to 85°; however, continuous ZnS films without any evident nanostructures were fabricated under normal deposition. The transmitting ability of ITO substrates coated with ZnS nanocolumn arrays is improved in comparison to bare ITO substrates and continuous ZnS films coated ITO substrates in the visible range. Organic light-emitting diodes (OLEDs) were simultaneously fabricated on these three kinds of substrates. The electro-luminescence (EL) intensity of OLEDs based on the ITO substrate coated with ZnS nanocolumn arrays was about 1.2 times bigger than the devices based on the other substrates (bare ITO substrates and continuous ZnS films coated ITO substrates) under the same driving voltage. The improvement of EL intensity should be ascribed to the enhancement of the light extraction by the nanocolumn arrays effect.