Structure and optical properties of electrochromic tungsten-containing nickel oxide films

Electrochromic Ni sub(x)W sub(1-x) oxide thin films with 0.5 < x < 1 were deposited by reactive DC magnetron co-sputtering from pure Ni and W metal targets. Films with different compositions were characterized structurally by X-ray diffraction. X-ray photoelectron spectroscopy and Rutherford backscattering spectrometry. The optical and electrochemical properties were investigated by spectrophotometry and cyclic voltammetry in LiClO sub(4) dissolved in propylene carbonate. Pure Ni oxide films were crystalline, but even small amounts of W led to amorphous structures. The Ni sub(x)Wi sub(1-x) oxide films probably consisted of hydrated Ni oxides and NiWO sub(4). Charge insertion/extraction and optical modulation were modest. Aging of the films led to strong bleaching. Concerning electrochromic properties, the W addition was beneficial and enhanced the bleached-state transmittance for all compositions at luminous and near-infrared wavelengths.