Structural and optoelectronic characterization of TiO₂films prepared using the sol–gel technique

Abstract

TiO 2 is a versatile material that makes for fascinating study in any of its several physical forms: monocrystal, polycrystal, powder or thin film. Its enhanced photosensitivity to UV radiation and excellent chemical stability in acidic and aqueous media point to its excellent potential for use in a variety of applications, such as solar cells, electronic devices, chemical sensors and photocatalysts. Of late, thin films of TiO 2 have permitted the study of physical and chemical properties that are almost impossible to examine in powders. Using the sol-gel technique, it was possible to prepare TiO 2 films, and to specifically modify their characteristic properties by means of annealing treatments. Optical measurements carried out on sol-gel derived films produced results similar to those found in films prepared using the sputtering technique. The use of TiO 2 films facilitates the study of the behaviour of crystalline structure, grain size, photoresponse, electrical conductivity in both darkness and light and energy band gap (E g ) as a function of treatment temperature. For the first time, it has been demonstrated that the photoconductivity of TiO 2 becomes apparent at a treatment temperature of 350 • C, which means that below this temperature the material is not photosensitive. The photosensitivity (S) of TiO 2 films prepared by the sol-gel technique reaches values between 10 0 and 10 4 , surpassing by more than two orders of magnitude the photosensitivity of TiO 2 in powder form. In addition, it was possible to study the surface crystalline structure, where TEM studies clearly revealed both the polycrystalline order and the atomic arrangements of the TiO 2 films. Our findings will afford us an opportunity to better study the nature of TiO 2 and to enhance its performance with respect to the above-mentioned applications.

Nanocrystalline TiO2 Thin Films Fabricated Via a Polyelectrolyte Multilayer‐Assisted Sol–Gel Reaction

“…For m 5 2, the indirect transitions of the electrons from the valence to the conduction band are allowed, while for m 5 1/2 the direct allowed transitions can be considered. [36][37][38][39] Near the absorption edge of the TiO 2 films, the best fit for direct allowed electron band-to-band transitions was obtained (Fig. 8).…”

“…To determine the optical band gap of the TiO 2 films, a general expression that relates the absorption coefficient (α) to the band‐gap energy was used >where m is the integer or semi‐integer, h is Planck's constant, h ν is the photon energy, and E g is the energy of the band gap. For m =2, the indirect transitions of the electrons from the valence to the conduction band are allowed, while for m =1/2 the direct allowed transitions can be considered 36–39 . Near the absorption edge of the TiO 2 films, the best fit for direct allowed electron band‐to‐band transitions was obtained (Fig.…”

Effect of Anatase Synthesis on the Performance of Dye-Sensitized Solar Cells

“…Then, a solution was added dropwise to the initial mixture that contained deionized water (5 ml), hydrochloric acid (3.75 ml), and ethanol (119.35 ml). The solution remained agitated for 24 h [13, 14]. The blocking layer was obtained by submerging and extracting transparent TEC15 conducting substrates (SnO 2 :F) in the precursor solution at a speed of 1.5 × 10 −3  m/s.…”

Dielectric Measurements on Sol–Gel Derived Titania Films

“…For example, the photosensitivity of sol-gel derived TiO 2 films annealed at 350°C was found to be higher than that of its powder by a factor as large as two orders of magnitude. 8 TiO 2 films became anatase in structure when subjected to heat treatment at 600°C, and the grain sizes were found to be smaller than those found for microwaveexposed films, resulting in the blue shift in UV-visible absorption spectra. 9 However, the sol-gel synthesis of TiO 2 nanoparticles was performed with room temperature ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate as a reaction medium, and the anatase phase was achieved without heat treatment.…”