Growth and characterization of titanium dioxide thin films by sol-gel spin coating and dip coating methods

Titanium dioxide is an advantageous metal oxide semiconductor material for solar cell applications such as photovoltaic and photocatalytic applications owing to its outstanding optoelectronic properties with good chemical stability. Researchers conducted studies to investigate and improve the characteristics of titanium dioxide thin films. In this study, titanium dioxide thin films were grown by sol-gel spin coating and sol-gel dip coating methods on glass substrate. The properties of the titanium dioxide thin films were investigated as a function of the aging time, layer number, and dipping time effect. For this purpose, the aging time, layer number and the dipping time changed as 1, 7, 14, 21, 28 and 56 days, 3, 5 and 10 layers and 5, 10 and 20 seconds, respectively. Besides that, to investigate the influence of annealing temperature on the thin film properties, the films were annealed at 300 °C, 400 °C, 500 °C, 600 °C, and 700 °C. According to the characterization results, all the titanium dioxide thin films were succesfully grown by Sol-Gel method. As-grown thin films and layers annealed at 300 °C were in amorphous form. The samples annealed at 400 °C and above were formed into a tetragonal anatase structure. The crystallization was increased in films annealed at 400 °C for both coating methods. Films by sol-gel dip coating contain isolated nano-sphere features according to top-down scanning electron microscopy images. Optical measurements showed that absorption thresholds shifted with changes in growth parameters. The bandgap values were calculated in the range between 2.97 – 3.63 electronvolt for all titanium dioxide thin films. The refractive index, dielectric constant, static dielectric constant, and porosity were improved with increasing annealing temperature. As a results it is found that the aging day, number of layers, dipping time and annealing temperature affected the structural, surface and optical properties of the titanium dioxide thin films.