Aging effect of diethanolamine stabilized sol on different properties of TiO2 films: Electrochromic applications

Diethanolamine derived clear precursor sol has been utilized for the deposition of TiO2 films annealed at 470 °C for 5 min. Effect of the precursor sol's aging on different properties of the films has been examined in the present study. Films obtained from aged sol have exhibited superior electrochemical (diffusion coefficient—2.46×10−10 cm2 s−1) and electrochromic characteristics due to enhanced Li ion insertion upon application of electric field. The aged sol derived films have exhibited a higher optical modulation (40% at 550 nm) between the colored and bleached states. The ion storage capacities of the films derived from freshly prepared and aged sols are 4.1 and 8.1 mC cm−2, respectively, upon applied voltage of ±1.5 V. X-ray diffraction studies have affirmed an increase in the TiO2 crystallite size upon the use of aged sol for the deposition of films. FTIR investigations have confirmed the conversion of Ti–O–Ti to Ti–O network in the aged sol derived films. SEM studies have evidenced porosity changes in films obtained from the sol aged for different durations. The index of refraction as measured by the ellipsometry method corroborates the SEM results and shows reduced porosity (pore size—38 nm) in films derived from the sol just reaching the state of gelation. Thickness of the aged sol derived film is measured to be the highest i.e. 350 nm. Energy bandgaps of the films for both direct and indirect transitions tend to decrease as a function of sol's aging.