Electrochromic dc Sputtered Nickel-Oxide-Based Films: Optical Structural, and Electrochemical Characterization

NiO films were made by dc magnetron sputtering of Ni in O2. The grain size was ~10 nm and the crystal structure was cubic. Subsequent electrochemical treatment in KOH established electrochromism. The material was studied by cyclic voltammetry, in situ measurements of optical transmittance and mechanical stress, spectral infrared reflectometry, and spectrophotometric measurements in the 0.35–2.5 μm range. Electrochemical data showed that electrochromic bleaching was associated with proton insertion. P-polarized infrared reflectance showed OH stretching vibrations representative of “free” OH for the bleached state and OH in the presence of hydrogen bonds for the coloured state. The luminous and solar transmittance could be varied between 80% and 20% and between 74% and 24%, respectively. The electrochromism is produced by absorption modulation.