Electrochromic properties of NiO _x :H films deposited by DC magnetron sputtering for ITO/NiO _x :H/ZrO ₂ /WO ₃ /ITO device

NiO _x :H thin films were deposited on ITO-coated glass by DC reactive magnetron sputtering at room temperature. The effects of the hydrogen content on the structure, morphologies, electrochemical properties, the stoichiometry and chemical states of NiO _x :H thin films were systematically studied. In X-ray diffraction and atomic force microscopy analysis, the crystallinity of the films tends to be weakened when the flow amount ratio of Ar:O ₂ :H ₂ equals 19:1:3 and as confirmed in electrochemical analysis, such relatively weak crystallinity is the main contributing factor to ion transportation. X-ray photoelectron spectroscopy reveals that the increase of the hydrogen contents results in a relatively lower binding energy exhibited in the Ni 2p spectra. The proportion of Ni ₂ O ₃ in NiO _x :H films increases from 22% at bleached state to 33% at colored state. A monolithic all-thin-film inorganic electrochromic device was fabricated with complementary configuration as ITO/NiO _x :H/ZrO ₂ /WO ₃ /ITO. The electrochromic device with optimized NiO _x :H thin films acting both as ion storage layer and proton-providing source displays high modulation efficiency of 68% at a fixed wavelength 550 nm.