Towards a thin films electrochromic device using NASICON electrolyte

The optimisation of the morphology of WO₃ thin films allowed a more efficient electrochromic colouring using Na⁺ ions than H⁺ ones. Therefore, sodium superionic conductor (Na₃Zr₂Si₂PO₁₂, NASICON) films may be used as electrolyte in inorganic electrochromic devices. In this paper, the structure, chemical composition, morphology and electrochromic properties of WO₃, ZnO:Al and Na₃Zr₂Si₂PO₁₂ thin films were studied to develop a novel type of electrochromic device. WO₃, ZnO:Al and Na₃Zr₂Si₂PO₁₂ thin films were deposited using reactive magnetron sputtering of tungsten, zinc and aluminium and Zr–Si and Na₃PO₄ targets, respectively. For transparent conductive oxide coatings, a correlation was established between the deposition parametres and the film’s structure, transmittance and electrical resistivity. Classical sputtering methods were not suitable for the deposition of NASICON films on large surface with homogenous composition. On the other hand, the use of high-frequency pulsed direct current generators allowed the deposition of amorphous films that crystallised after thermal annealing upon 700 °C in the Na₃Zr₂Si₂PO₁₂ structure. Amorphous films exhibited ionic conductivity close to 2 × 10⁻³ S cm⁻¹. Finally, preliminary results related to the electrochromic performance of NASICON, WO₃ and indium tin oxide devices were given. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, France, Sept. 9–15, 2007.