Structural, optical and electrochemical properties of sol–gel derived TiO2 films: Annealing effects

Sol–gel derived TiO2 films deposited using spin-coating technique and annealed at different temperatures from a precursor sol based on titanium isopropoxide and diethanolamine (stabilizing agent) in ethanol have been investigated by a wide range of techniques. The influence of aging of the sol on the electrochemical properties of 400 °C annealed films has also been studied. In comparison to the films prepared from a freshly prepared sol, the diffusion coefficient, ion storage capacity, and optical modulation of the films deposited from the sol just before gelation are observed to be superior. Structural analysis performed on the films provides evidence for the appearance of crystallinity to be dependent on firing temperature with the anatase phase being first detected in the films annealed at 300 °C. The electrochromic behavior is seen to prevail in both amorphous and the nanocrystalline films, though relatively slower switching kinetics is observed for the amorphous film. The comparison of the electrochromic response between the films annealed at different temperatures has shown that the best response is exhibited by the 400 °C annealed film owing to its highest ion storage capacity and a highly porous structure, which includes optimum sized nanograins. The correlation between the structure and electrochromic property is clearly evident from these studies.