Electrochromic properties of nickel oxide based thin films sputter deposited in the presence of water vapor

Electrochromic nickel oxide based thin films were prepared by reactive RF magnetron sputtering from metallic nickel in the presence of Ar, O2 and H2O. The water vapor led to enhanced optical modulation and charge capacity. At a wavelength of 550 nm the bleached state transmittance was 0.73 and the transmittance for the colored state was 0.28 and 0.15 for water partial pressures of pH2O < 10−3 Pa and pH2O ~ 7 × 10−2 Pa, respectively. The charge densities were 14 and 25 mC/cm2 for pH2O < 10−3 Pa and pH2O ~ 7 × 10−2 Pa, respectively. The coloration efficiency was decreased with increased water partial pressure, from about 0.07 to 0.06 cm2/mC. Preliminary results show that the H2O promotes an amorphous structure and makes the films increasingly hydrous.