Stable inks for inkjet printing of TiO2 thin films

In recent years, inkjet printing has been found to be a very promising and useful method for material deposition, and even semiconductor films can be deposited directly from a colloidal dispersion (ink) onto a large variety of substrates. The ink properties, such as solvodynamic particle size, zeta potential, isoelectric point, jetting performance, wetting and adhesion on substrates, should be optimized in order to achieve uniform deposition. In this work, the preparation of very stable colloidal dispersions based on TiO2 in three different crystal phases is presented. TiO2 has received a lot of attention because of its potential application in electronic devices. TiO2 inks were characterized by dynamic light scattering (DLS) measurements and the results show that the average solvodynamic particle size is around 25, 32 and 28 nm for anatase, rutile and brookite, respectively. The films obtained by inkjet printing were characterized by X-ray diffraction analysis, scanning electron microscopy, and UV-Vis spectrophotometry. The results show that the inkjet printed films were uniform, with thicknesses of 70, 140 and 130 nm for anatase, rutile and brookite, respectively. The current-voltage characteristics of conducting oxide-TiO2-Ag devices show diode behavior, confirming the semiconductor nature of the TiO2 films prepared by the inkjet printing technique. The ink preparation procedure reported in this work allows for the deposition of homogeneous and uniform films of all three phases of TiO2, and their potential for application in electronic devices.