Transparent electrode for OLEDs

The thin films of transparent conducting oxides (TCOs) have widespread applications due to their unique properties of good electrical conductivity and high optical transparency in the visible spectrum range. There have been a great deal of activities in the development of TCOs for a variety of applications. In general, properly doped oxide materials, e.g., ZnO, SnO2, and In2O3, are used individually or in separate layers or as mixtures such as indium tin oxide (ITO) and indium zinc oxide (IZO) for making TCO thin films. ITO, aluminum-doped zinc oxide (AZO), and fluorine-doped tin oxide (FTO) are commonly used TCO materials for different applications. The distinctive characteristics of these TCOs have been widely used in antistatic coatings, heat mirrors, solar cells [1,2], flat panel displays [3], sensors [4], andorganic light-emitting diodes (OLEDs) [5-7]. The properties of TCO films are often optimized accordingly to meet the requirements in the various applications that involve TCO. The light scattering effect due to the usage of textured TCO substrates helps to enhance the light absorbance in thin-film amorphous silicon solar cells [8,9]. However, a rough TCO surface is detrimental for OLED applications. The localized high electric fields induced by the rough TCO surface can cause a nonuniform current flow leading to the dark spot formation or a short device operation lifetime.