Properties of Nanostructured Rutile Titanium Dioxide (TiO<sub>2</sub>) Thin Film Deposited with Silver Sulfide (Ag<sub>2</sub>S) Quantum Dots as Photoanode for Solar Photovoltaic

Abstract

Titanium dioxide (TiO2) nanoparticles thin film has been successfully prepared by a simple hydrothermal process using Hydrochloric Acid (HCl) as chelating agent and Titanium (IV) Chloride (TiCl4) as precursor. In this study, the nanostructured TiO2 thin films were prepared at different hydrothermal reaction times of 2 hours, 5 hours, and 10 hours, and then Ag2S Quantum Dots (QDs) were deposited on the surface of TiO2 nanoparticles using 6 cycles of Successive Ionic Layer Adsorption and Reaction Deposition (SILAR) method. The surface morphology, crystalline structure and optical characterizations of the films were carried out using Field Emission Scanning Electron Microscopy (FESEM), Atomic Force Microscope (AFM), X-ray Diffraction (XRD) and Ultra-Violet-Visible Near Infrared Spectrophotometer (UV-Vis). For electrical properties, four-point probe investigated the sheet resistance, resistivity, and conductivity of these thin films. TiO2 nanorods were formed with diameter ranged from 33.78 nm to 42.58 nm and the length of TiO2 layer increased as the reaction time increased, from 2.84 μm to 3.93 μm (without Ag2S QDs) and 2.88 μm to 4.85 μm (with Ag2S QDs). When the reaction time reaches 10 hours, nanoflowers can be seen on the surface of film. The XRD results showed that with longer reaction time, the value of full-width at half maximum (FWHM) of the TiO2/ Ag2S QDs thin films decreased from 0.335° to 0.263 while the crystallite size increased from 22.73 nm to 35.39 nm. UV-Vis analysis indicated that the optical band gap of these thin films decreased from 2.68 eV to 2.00 eV (direct) and 2.94 eV to 2.40 eV (indirect) with increased in reaction time. The electrical properties of the films showed that the resistivity varied between 7 x 107 Ω.cm and 5.07 x 107 Ω.cm when the reaction time changed from 2 hours to 10 hours. The conductivity of the TiO2/ Ag2S QDs thin films increased with the increase in hydrothermal reaction time and further increased with the incorporation of Ag2S QDs. Besides, the TiO2 films synthesized hydrothermally for 10 hours showed higher surface roughness as compared to other thin films. The obtained results showed that the TiO2 / Ag2S QDs thin films are applicable as a photoanode for Quantum Dots Sensitized Solar Cell (QDSSCs) applications.