Modification of optical properties of spin-coated TiO2 film by heat treatments

In this report, effects of heat treatment conditions on the transmittance of titanium dioxide, TiO₂, films were examined. The colloidal solution of TiO₂ in two different solvents – isopropanol, IPA, and sulfuric acid, H₂SO₄, were deposited via a spin-coating method onto clean glass substrates. The films were subsequently annealed and cooled down, either quickly or slowly, before being measured for their optical transmittances in the visible region. Three points were noted: Firstly, when the films were quickly cooled down after annealed, their transmittance depended on their annealing temperature. In IPA and H₂SO₄, the transmittance decreased and increased, respectively, when the annealing temperature increased. Secondly, when the films were slowly cooled down after annealed, their transmittance seemed to be independent from the annealing temperature, where the films had roughly equal transmittance regardless of annealing temperature. Lastly, the TiO₂ films with H₂SO₄ provided higher transmittance than those with IPA. All the three stated characteristics were the same for all wavelengths in the visible region. These results were believed to result from the dispersibility of the TiO₂ in each solvent and the cooling-down processes. Such results could be further developed to select a suitable heat treatment process for a spin-coated TiO₂ film with a desired optical transmittance.