Transparent Conductive Oxide (TCO) Films for Organic Light Emissive Devices (OLEDs)

Abstract

Transparent conducting oxide (TCO) thin films of In2O3, SnO2, ZnO, and their mixtures have been extensively used in optoelectronic applications such as transparent electrodes in touch panels, flat panel displays (FPDs), and other future devices. The first chapter provides an introduction to the basic physics of TCO films and surveys the various topics and challenges in this field. It includes a description of the TCO materials used in some of the organic light emissive devices (OLEDs) that have been studied extensively to date, the performance of various OLEDs, and a brief outlook. Chapter 2 focuses on TCO material development of p-type and n-type. Typical oxide kind of TCO materials consist of In2O3, SnO2, and ZnO. These are applied as a TCO films with ntype semiconducting property according to highly doped dopants which acting as a carrier. Until today, in a n-type TCO materials, indium tin oxide (ITO) doped with SnO2 of 10 wt.% in In2O3 has been widely commercialized. This is because the ITO film has high performance of both good electrical conductivity of ~10-4 Ω·cm and high transmittance of ~90% when the ITO film is coated on glass substrate. At present, In2O3-SnO2 (ITO) films are most commonly used as TCO films, but they have ome disadvantages, such as high cost, instability, poor surface roughness, and toxicity in their further applications. And amorphous ITO film deposited at low temperature has low resistance under moist heat, which leads to a decrease in its conductivity and light transmittance. In addition, unfortunately, the price of Indium is dramatically increasing every day due to a mix-up between the supply and demand of raw materials by the exhaustion of Indium source. On the other hand, some zinc-based TCO materials have good optical and electrical properties comparable to the ITO films, as well as low cost, high stability, excellent surface uniformity, and good etching selectivity. The zincbased TCO films are, therefore, regarded as promising substitutes for ITO film. In Chapter 3, the Indium-based and Zinc-based TCO Materials, and their electrical, optical, and structural properties will be discussed. Particularly, since more stringent specifications for TCO films have been required for realization of both higher resolution and larger screen size of FPDs, and preparation of high-quality TCO films at low temperature is very important to realize advanced optoelectronic devices. Chapter 4 will introduce the new TCO materials, such as: organic conductors like poly(3,4ethylenedioxy thiophene):poly(styrenesulphonicacid) (PEDOT:PSS), and the expanding field of nanomaterials including carbon nanotubes, nanoparticles, and composite materials combining one or more of these materials. For example, long metallic nanotubes have been