Influence of Post Annealing Rates on Porosity, Dispersion Energy and Associated Dielectric Energy Losses of TiO₂ Thin Films

With scientific and technological advances, Titanium dioxide (TiO₂) has attracted great research interest in the field of Dye Sensitized Solar cells (DSSC) with an aim to improve its efficiency. In this study, transparent semiconducting titanium dioxide thin films were deposited on glass substrate coated with fluorine tin IV oxide (SnO₂: F) film by sol gel technique. The films were then annealed in air up to 450°C at different annealing rates. Optical reflectance was measured using UV-Vis-NIR spectrophotometer and optical parameters such as refractive index, extinction coefficient and dielectric constants were modelled using SCOUT software. Average refractive indices in the visible region ranged between 1.95 and 1.56. Porosity for as deposited, 1 step, 2°C/min and1°C/min were found to be 48%, 73%, 61% and 53% respectively. Refractive index dispersion was investigated using Wemple – Di-Domenico single oscillator model. Dispersion energy of annealed films increased from 5.90 eV to 11.30 eV. Surface and volume energy loss were computed from dielectric constants and correlated with porosity and dispersion energy as function of the heat treatment. Optical parameters were found to highly depend on the annealing the thin films. Annealing rate influenced a decrease in porosity and an increase in dispersion energy due to film densification and pore filling as the crystallinity is improved by heat treatment.