Fabrication and Properties Studies of Cu-doped NiO Electrochromic Thin Films
|School||Ocean University of China|
|Course||Materials Physics and Chemistry|
|Keywords||Cu-doped NiO film electrochemical deposition electrochromic transmittance|
Electrochromism （EC） materials, which can reversibly change their optical properties （transmission, reflection and absorption） under an applied electric field, have been widely used in producing display, dimming glasses and information storage devices. They have aroused a great interest in information, electron, energy sources, architecture, national defense etc. due to their excellent performance of continuous and reverse photoelectric properties induced by electrochemical proeesses.EC materials can be classified into two categories as anode colored and cathode colored materials by their electrochemical reaction modes. Among various EC materials, nickel oxide （NiO）, as a representative of the anode colored materials, is able to change its color from transparent in the reduced state to a deep brown black in the oxidized state reversibly when a positive/negative potential is applied. Hence, NiO is now considered to be one of the best electrochromic performances for its high coloration efficiency, strong reversibility, short response time and long cycle life. However, it is still far from practice use because of its some shortcomings. There are some ways to improve the electrochromic performance of the film, for instance, optimizing process parameters and doping method are two effective ways.There are several preparation processes for electrochromic films such as sputtering deposition, vacuum-evaporation, pulsed laser deposition and sol-gel, among which electrochemical deposition is the most optimal preparation process, for its merits of lower requirement of equipments, and the films need not to be subjected to an annealing process in order to show electrochromic properties. However, there are relatively few reports on preparing NiO films by electrochemical deposition.In the paper, Cu-doped NiO film is prepared on the surface of FTO conducting glasses using electrochemical method with NiCl2 as main salt, CuCl2 as dopant and LiClO4 as supporting electrolyte from organic solution of N, N-dimehtyl formamide （DMF）. Effects of parameters, such as doping dosage, deposition time, deposition voltage and annealing temperature were discussed. To find the porcedure associated with the formation of the film with the best electrochromic properties, following researches and experiments were carried out: to compare the visible light transmittance （ΔT ） of the colored state with the bleached state of the eleetrochromic films, to count the dynamic of optical density change （ΔO D）, and to test the response time and CV curves. The morphology, structure, capacity of colored storage and cycle life were also characterized.Results show that, when Cu: Ni=1:10, the deposition time is 15 min and deposition voltage is 3.5 V, the Cu-doped NiO film has excellent electrochromic properties withΔT =88.8% andΔO D=1.063, tb/ts=4.53/2.61 s and EC= 42.45 mC/cm2. Its cycle life was at the same level as the undoped NiO film. However, heat-treatment was found to reduce the electrochromic properties of the film, and the film almost lost the electrochromic ability at 600℃. In addition, the Cu-doped NiO film exhibited excellent color memory and storage ability in air but poor in alkali solution. According to the SEM, XRD and FTIR analysises, the electrochromic mechanism of the Cu-doped NiO film was proposed.