Electrochromic Behavior of Ni1-xO Thin Films in Various Electrolytes
Ni1-xO thin films were grown at room temperature by sputtering deposition on ITO-glass substrate. The influence of various partial pressures of O2 (a 4 Pa total pressure was maintained during deposition) on the stoichiometry, morphology and cristallinity of Ni1-xO thin films was studied and correlated to their EC behavior. Unsurprisingly, an increase in oxygen partial pressure is related to a stronger brownish appearance associated with to an increase in the Ni3+ amount as well as a decrease in film porosity and roughness. Moreover, the comparison of the electrochemical properties of Ni1-xO films cycled in aqueous (KOH), lithium based and lithium free ionic liquid electrolytes, shows an evolution from a faradic to a pseudo-capacitive behavior, while optical contrast from colorless to brownish remains in all cases. This suggests that electrochromism is not only the result of of small cations (de)insertion but also depends on surface phenomena including possible participation of anions.
Herein, the relationship between the physical-chemical properties and EC performances of non-stoichiometry Ni1-xO thin films will be investigated. Finally, the combination of Ni1-xO with WO3 and PEDOT in full devices will be discussed.
 C.G. Granqvist, Handbook of inorganic electrochromic materials, Elsevier, Amsterdam, Netherlands, 1995