. 2009, 27(0918): 66-70.
Electrochromism can be defined as a persistent and reversible optical transformation induced by electrochemical processes. Electrochromic (EC) materials can reversibly change their optical properties upon charge insertion/extraction, usually with low power consumption, high Coloration Efficiency (CE), and excellent memory effect under an open circuit condition. Hence they have received great attention in the past decades. EC materials can be classified into two categories as anode colored and cathode colored materials by electrochemical reaction modes. As a kind of anode colored materials, NiO is one of most attractive materials due to its high electrochromic efficiency, large dynamic range, good cyclic reversibility, and low cost. Several physical and chemical methods have been used to fabricate nickel oxide films. For example, sputter coating, vacuum evaporation, pulsed laser deposition, spray pyrolysis, sol-gel, chemical deposition and electrochemical deposition. However, the materials prepared by above methods must subject to an post-annealing process in order to show electrochromic properties. In this paper, NiO thin films with reversible electrochromic properties are fabricated using electrochemical technique in organic solutions (N,N-dimethylformamide solution, DMF solution) controlled by potentiostatic electrolysis. Fluorine-doped tin oxide (SnO2:F, FTO) glass plates are used as substrates as well as cathodes. Appropriate experimental conditions for the film deposition are chosen based on our investigation on the effect of solvent dehydration methods and electrodeposition voltages. XRD, SEM, HRTEM and EDS are employed to analyze the composition, structure and thickness of the films. Ultraviolet-visible transmission spectroscopy is applied to measure electrochromic properties of the deposited films. Cyclic voltammetry and double potential step technique are used to study the electrochromic processes.
