Printing of Ultrathin Nanoparticulate Indium Tin Oxide Structures

Abstract

This contribution focusses on three printing techniques: inkjet printing, flexographic printing and gravure printing for the manufacture of ITO structures based on nanoparticular ITO inks. The quality and stability of nanoparticular inks depends mainly on the dispersing step and is reflected by the achieved particle size distribution. The particle size distribution of the ITO inks has a distinct influence on the optical and electrical properties of the deposited ITO structures. The optimization of nanoparticular ITO inks concerning rheological behavior, wetting behavior and resulting material performance is presented. Inkjet printing was used as a low speed method to manufacture structures in the range of 30 μm. It is shown how coffee-staining, a frequently arising problem in inkjet printing, can be prevented by different strategies. Nanoparticular ITO structures with layer thicknesses clearly below 1 μm were printed. Gravure and flexography printing are well-established industrial printing processes with printing speeds above 100 m/min. These high-speed printing processes were used to print structures on PET film and glass substrates. Different solvents, e.g., water and ethanol, solvent compositions and binder types were varied to optimize the resulting ITO structures. The printed structures in the range of 10 to 2000 μm with thicknesses down to 1 μm were evaluated concerning surface topography and electrical conductivity. The high inter-grain porosity and the used organic additives limit the electrical conductivity of nanoparticulate ITO structures. To further improve their electrical conductivity laser post-treatment of printed ITO structures was performed.