Electrochromic properties of iridium oxide thin films prepared by reactive sputtering in O2 or H2O atmosphere

Abstract

Iridium oxide is an electrochromic (EC) material, i.e., it shows reversible and persistent changes in optical properties. In this study, the authors investigated the effects of substrate temperature and sputtering gas on the structures and EC properties of iridium oxide thin films prepared by reactive radio-frequency magnetron sputtering. An Ir metal target was sputtered in an O2 or H2O atmosphere at substrate temperatures between −30 and 130 °C. The crystal structures and chemical bonding states of the films were examined using x-ray diffraction and Fourier-transform infrared (IR) spectroscopy, respectively, and their EC properties were studied in 0.5 M aqueous H2SO4 electrolyte solution. IrO2 films were deposited at 70 and 130 °C, and amorphous films were formed at 20 and −30 °C in both O2 and H2O atmospheres. IR absorption peaks from hydrogen-bonded OH groups were clearly observed for films deposited in an H2O atmosphere at substrate temperatures of −30 and 20 °C, which indicates that iridium oxyhydroxide or hydrated iridium oxide films were deposited. The amorphous iridium oxyhydroxide or hydrated iridium oxide films showed large variations in transmittance and high bleached-state transmittances, and they are considered to be suitable for use in EC devices.