Synthesis, and Impact of Annealing Rates on the Physical and Optical Properties of Spin Coated TiO₂ Thin Films for Renewable Energy Applications

High-performance titanium dioxide (TiO₂) thin films were successfully produced and deposited on a circular glass substrate using the spin coating process at room temperature. The deposited films were subjected to annealing at temperatures of 300, 800, 900, 1000 and 1100 °C to investigate the temperature-dependent changes in their physical characteristics. Analysis techniques, including scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, Fourier transform infrared spectroscopy, and ultraviolet–visible transmittance spectroscopy, were employed to examine the properties of the TiO₂ films. The SEM images revealed that the films were homogeneous, consistent and dense, exhibiting minimal presence of pores and microcracks. AFM scans demonstrated that the film surfaces were uniformly smooth, with a roughness ranging from approximately 0.52 to 2.85 µm. Additionally, SEM analysis indicated that the films were crack-free, homogeneous and composed of fine grains with an average size of approximately 50 nm. The UV spectral results unveiled important optical changes in the films. The Urbach energy exhibited an increase from 1.47 to 2.5 eV, while the direct band gap energy showed a decrease from 3.90 to 3.03 eV. Regarding the hydrophilicity of the TiO₂ films, the sample annealed at 300 °C displayed the lowest water contact angle among all tested samples. However, the hydrophilicity of anatase TiO₂ thin films increased when subjected to annealing temperatures between 400 and 800 °C. Conversely, the presence of the rutile phase resulted in a reduction in hydrophilicity when the annealing temperature ranged from 900 to 1100 °C. It was found that by using annealing, thin spin coated TiO₂ films will be more uniform and transparent. These results demonstrate the suitability of the obtained TiO₂ films for use in solar cells, further supporting their potential for practical applications.