Electrochromic screen-printed tungsten trioxide electrodes

A methodology is presented to develop tungsten-oxide based inks for screen-printing. Different amounts of tungsten oxide have been grown by co-precipitation on the surface of conducting microparticles. These modified particles have been formulated into inks, and electrodes have been screen-printed. The work describes the characterization of the materials using a range of techniques including XRD, SEM, as well as electrochemical and spectroscopic techniques. Thermal treatment of the co-precipited oxides changes their crystalline structure, increasing bandgap (from 2.48 eV to 2.87 eV) and worsening their electrochromic performance. Structures printed with untreated WO3-based materials display contrast ratios as high as 90 % in reflectance, and colour efficiencies between 30 and 40 cm2 C-1. Another important aspect is the pH stability of the oxide up to pH = 6.