Electrochromic Behavior of Vanadium Pentoxide Thin Films Prepared by a Sol-Gel Spin Coating Process

Herein, the synthesis of vanadium oxide thin films with high electrochromic coloration efficiency through a simple sol-gel spin coating technique is reported. The structural studies confirm the formation of V2O3-V2O5 mixed phase at 250 degrees C and the pure beta-V2O5 phase at 350 and 450 degrees C. The decrease in optical bandgap, refractive index, and extinction coefficient improves the transmission ability of the films at higher temperatures. The photoluminescence emission peak observed at 553 nm is due to the recombination of electron-hole pair intrinsic transition from the lowest split-off V 3d band to the O 2p valence band. The tuning of surface morphology from rod to platelet structure may be due to the higher annealing temperature which assists the disorder movement of the particles. The observed V 2p core levels confirm the existence of V5+ oxidation state with the splitting of 7.2 eV. The electrochromic behavior of vanadium oxide film is detected in 0.5 m LiClO4 in propylene carbonate electrolyte solution. The results show that the film annealed at 450 degrees C exhibits high coloration efficiency of 110.98 cm(2) C-1, good reversibility of 99%, and faster switching speed for bleaching (2.1 s) and coloration (2.4 s) processes.