Inkjet printing of sol–gel derived tungsten oxide inks

• The first report of inkjet printed transparent WO3 layers.
• Development of WO3 sol–gel ink for piezoelectric inkjet printing.
• Tuning of rheological/physicochemical properties of WO3 inks by solvent combinations.
• Demonstration of an electrochromic device incorporating a WO3 printout.

Tungsten (VI) oxide−WO3 is a widely studied functional inorganic semiconductor material with exceptional chromogenic properties. It is used in energy efficient systems such as smart windows, sensors, displays, storage units, photocatalysts and solar cells. Layers of WO3 are generally produced using expensive vacuum deposition techniques. In this paper, the inkjet printing of sol–gel derived tungsten inks on glass and transparent conductive oxide is reported. Peroxo sol–gel synthesis was used to prepare peroxopolytungstic acid sols which were then modified using different solvents to obtain a suitable jetting ink. Described are the rheological and structural properties of WO3 inks, the dynamics of WO3 droplets and the morphology and quality of WO3 printouts. The functionality of these transparent WO3 layers is successfully demonstrated in an electrochromic device.