Using an Atmospheric Pressure Chemical Vapor Deposition Process for the Development of V2O5 as an Electrochromic Material
Vanadium pentoxide coatings were grown by atmospheric pressure chemical vapor deposition varying the gas precursor ratio (vanadium (IV) chloride:water) and the substrate temperature. All samples were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, cyclic voltammetry, and transmittance measurements. The water flow rate was found to affect the crystallinity and the morphological characteristics of vanadium pentoxide. Dense stacks of long grains of crystalline
... ains of crystalline oxide are formed at the highest amount of water utilized for a substrate temperature of 450 • C. Accordingly, it was indicated that for higher temperatures and a constant gas precursor ratio of 1:7, the surface morphology becomes flattened, and columnar grains of uniform size and shape are indicated, keeping the high crystalline quality of the material. Hence, it was possible to define a frame of operating parameters wherein single-phase vanadium pentoxide may be reliably expected, including a gas precursor ratio of 1:7 with a substrate temperature of >450 • C. The as-grown vanadium pentoxide at 550 • C for a gas precursor ratio of 1:7 presented the best electrochemical performance, including a diffusion coefficient of 9.19 × 10 −11 cm 2 ·s −1 , a charge density of 3.1 mC·cm −2 , and a coloration efficiency of 336 cm 2 ·C −1 . One may then say that this route can be important for the growth of large-scale electrodes with good performance for electrochromic devices. Coatings 2017, 7, 24 2 of 10 based on solution can hardly be up-scaled, due to the long reaction period, toxic reducing agents, and large amount of solvent required. Additionally, methods such as sputtering are not compatible with on-line manufacture. Hence, a low-cost, simple, and easily integrated into float-glass production lines technique is required. As with many coatings, chemical vapor deposition (CVD) routes are more attractive for the production of vanadium oxides on glass than other conventional techniques, since the stoichiometry and the morphology of the coatings can be simply controlled by tuning the vapor flows in the coating zone [18, 19] . In addition, the simplicity of CVD-particularly when performed at atmospheric pressure (APCVD)-makes such a process compatible with on-line glass manufacturing processes. Nevertheless, there are very few reports related to APCVD electrochromic V 2 O 5  . The aim of this work is to define a frame of APCVD operating parameters wherein single-phase V 2 O 5 may be reliably expected to form. Additionally, a correlation of the morphological characteristics with the corresponding electrochemical/electrochromic performance of the coatings is highlighted, which is important for the understanding and the enhancement of Li + intercalation into the vanadium oxide matrix.