Influence of Ag-doping on Optical and Structural Properties of TiO2 Thin Films Deposited by Electrohydrodynamic Spray Pyrolysis

Abstract

Aims: To study structural and optical properties of undoped titanium (IV) oxide (TiO2) and doped with 1.0 and 1.5M of silver. Study Design: Electro- hydrodynamic spray pyrolysis technique was used. Place and Duration of Study: titanium acetyl acetonate [Ti(C5H7O2)4], propanol [C3H8O] and silver nitrate [AgNO3] was obtained from Sheda Science and Technology Complex (SHESTCO) Abuja (Nigeria). The study was carried out between March 2017 and November 2017 at Sheda Science and Technology Complex (SHESTCO) Abuja (Nigeria). Methodology: TiO2 was synthesized using 0.2mol of titanium acetyl acetonate [Ti(C5H7O2)4] and 20mol of propanol [C3H8O] as the precursor. The silver (Ag) was obtained using 0.68 g of silver nitrate [AgNO3], mixed with 20 mol of propanol in a conical flask and placed on a magnetic stirrer. The flow rate by volume was set at 4200 microlitres/hour and the time of deposition was set at 10 min. The Electro-hydrodynamic Spray Pyrolysis Technique was set at voltage of 3.5 KV and the distance between the nozzle and the substrate (pre-cleaned glass) was 5.95 mm. Undoped TiO2 and doped with1.0 and1.5M of silver was deposited at 250ºC. Results: The films were characterized by Surface Profilometry, Ultraviolet – Visible light Spectroscopy (UV-Vis Spectroscopy) and X-ray diffraction (XRD). The results from surface profilometry showed that all the samples were thin films in the range of 300 to 700 nm. XRD results reviewed crystalline structure of TiO2. Crystal phase observed for both TiO2 and silver-doped TiO2areanatase structure. These results of (UV-Vis Spectroscopy) show that the undoped TiO2 exhibited low absorbance within the visible spectrum but increased as we dope with 1.0 M and 1.5 M of silver. The results also showed that all the films have high transmittance around 50- 95% in the visible region and NIR of the spectrum such that we can use them as optical windows in solar cell. The undoped TiO2 has the highest transmittance and is observed that the optical transmittance decreases with increasing Ag. Extinction coefficient increases within the visible region as we doped and the results also showed that the absorption coefficient, the direct transition and indirect transition can be controlled. The study of the microstructural properties using Optical Microscopy showed increase in the number of orderly stacked grains as we doped with Ag and average particle sizes are between 6 μm and 8 μm.The direct band-gap for the films range from 3.81 eV- 3.00 eV while the indirect band-gap for the films range from 3.80 eV – 2.60 eV. The energy gap is decreased gradually as doping increases.