Electrochromism in composite WO3–Nb2O5 thin films synthesized by spray pyrolysis technique

Abstract

Composite WO 3 -Nb 2 O 5 thin films were deposited on the glass and fluorine-doped tin oxide (FTO)-coated glass substrates using simple and inexpensive spray pyrolysis technique. The process parameters, like nozzleto-substrate distance, spray rate, concentration of sprayed solution, etc., were optimized to good quality films. The films were characterized for the structural, morphological, optical, and electrochromic properties. Structural and morphological characterizations of the films were carried out using scanning electron microscopy and X-ray diffraction techniques. Electrochemical properties of the Composite WO 3 -Nb2O 5 thin films were further studied using cyclicvoltammetry, chronoamperometry, chronocoulometry, and electrochemical Impedance spectroscopy.

Film Deposition of Electrochromic Metal Oxides through Spray Coating: A Descriptive Review

“…The spray deposition of WO 3 films for EC applications has been covered in about 45 publications since 1986, including 25 (14) over the last 10 ( 5) years (Table 1). Notable initiatory works were conducted by K. Colbow et al in the late 1980s and early 1990s [72][73][74][75], reporting the spray pyrolysis deposition at 400 • C of polycrystalline WO 3 layers from solutions of tungsten chloride WCl 6 dissolved in ethanol or dimethylformamide DMF, resulting in 250 to 650 nm thick films showing up to 73% (75-2) of optical contrast in VIS and coloration times of 40 to 60 s. New developments in pyrolytic spraying were achieved in the 2000s [76][77][78][79][80][81][82][83][84][85][86][87][88][89], notably by P. Patil and co-workers who addressed multiple compositions of precursor solutions-the combination of WO 3 with other oxides (MoO 3 , TiO 2 , Nb 2 O 5 ), the nature of W salt (mostly tungstates, being less corrosive and toxic than chloride derivatives) and/or the solvent (mostly water), etc.-and of substrate temperatures during and/or after the deposition process (as annealing post-treatments), being between 300 and 525 • C (typically 450 • C). Films of thickness between 200 and 750 nm were consecutively obtained, presenting moderate VIS contrasts ∆T (up to 50%) but quite fast commutation kinetics (t col and t ble less than 10 s), and tested over 1000 to 2000 cycles; high coloration efficiency CE values were particularly noticed for mixed WO 3 -MoO 3 formulations (42-63 cm 2 /C) [79] and for WO 3 layers included with multi-walled carbon nanotubes (43-79 cm 2 /C) [85].…”

A Brief Overview of Electrochromic Materials and Related Devices: A Nanostructured Materials Perspective

“…Sol-gel methods make it possible to produce large-area WO 3 films at lower cost in comparison with traditional vacuum methods [119]. The advantages of this method include: universality of sol-gel processes, easy control of microstructure and composition under low-temperature conditions, relatively simple and inexpensive equipment, control of microstructure, crystal size, porosity and composition of the deposited films, which is important, since these characteristics affect thin film kinetics, durability and staining efficiency [120]. However, many problems still remain to be solved, among them solution stability, large-area uniformity, insufficient adhesion, insufficient film thickness, and low repeatability.…”

Understand the Degradation Mechanism of Electrochromic WO3 Films by Double‐step Chronoamperometry and Chronocoulometry Techniques Combined with in situ Spectroelectrochemical Study

“…Usually, the chronoamperometric technique was only used to estimate the single-cyclic charge capacity of the electrochromic films as well as the switching speed of the electrochromic film from one state to another state [19][20][21][22][23][24]36]. Currently, the primary method that has been adopted by most researchers to characterize the electrochromic performance of materials is cyclic voltammetry.…”

“…Certainly, it can meet the basic test requirements, such as multi-cycle test, coloration/bleaching controlling and calculating charge capacity, etc. Double-step techniques involving chronoamperometry and chronocoulometry have been employed to estimate the single-cycle response time and charge capacity of electrochromic films [19][20][21][22][23][24]. These bring about that the factors effecting electrochemical reaction of the film are unclear, and consequently, the measures adopted to improve the electrochromic performance are inaccurate.…”