Effects of Cl2 plasma treatment on stability, wettability, and electrical properties of ITO for OLEDs

Abstract

We investigated various characteristics of chlorinated indium tin oxide (Cl-ITO) for highly efficient organic light-emitting diodes (OLEDs): the work function, surface morphology, wetting characteristic, and hole-injection property. Via the systematic analysis of Cl-ITO, we showed that the modification of ITO using the plasma treatment method has a simple process and offers higher stability than that achieved with a solution-based modification method. We fabricated Cl-ITO with a high work function of 6.04 eV, which is 1.04 eV higher than that of pristine ITO. We verified that Cl2 plasma treatment does not affect the ITO surface morphology. The Cl halogenated surface showed a low surface polarity and influenced the growth of the organic material, especially for films as thin as ∼4 nm. Therefore, we found when using ultra-thin film on Cl-ITO for design devices, the wetting characteristic of Cl-ITO should be considered. In addition, using tris-(4-carbazoyl-9-ylphenyl)-amine resulted in increased current and power efficiencies compared with those obtained using 4,4′-N,N′-dicarbazolebiphenyl. When a carrier-only device was used, the carrier-injection characteristics of Cl-ITO were higher than those of other well-known hole-injection materials. Furthermore, the Cl-ITO OLEDs showed higher stability than OLEDs with other hole-injection materials.