Photovoltaic Performance of Spherical TiO 2 Nanoparticles Derived from Titanium Hydroxide Ti(OH) 4 : Role of Annealing Varying Temperature

High-quality titanium dioxide (TiO 2 or titania) nanoparticles (TiO 2 NPs) with tailored morphologies are desirable for efficient photovoltaic applications. In this view, some thin films containing spherical TiO 2 NPs were prepared on indium tin oxide (ITO) and silicon (Si) substrates from titanium hydroxide Ti(OH) 4 using the unified sol-gel, spray and spin coating method followed by thermal annealing at different temperatures (in the range of 200–650 °C). Samples were characterized using various analytical tools to determine the influence of annealing temperatures on their structures, morphologies, and optical and photovoltaic characteristics. A field-emission scanning electron microscope (FESEM) and energy-filtered transmission electron microscopy (EFTEM) images of the annealed films displayed the existence of spherical TiO 2 NPs of average size in the range of 3.2 to 33.94 nm. XRD analysis of the films showed their amorphous nature with anatase and rutile phase. Optical UV-Vis spectral analysis of the annealed films exhibited a decrease in the bandgap energy from 3.84 to 3.24 eV with the corresponding increase of annealing temperature from 200 to 650 °C. The optimum films obtained at 500 and 600 °C were utilized as electron transport layers to fabricate the metal-insulator-semiconductor solar cells. The cells’ power conversion efficiency assembled with the spherical TiO 2 NPs-enclosed thin films annealed at 500 and 600 °C were 1.02 and 0.28%, respectively. Furthermore, it was shown that the overall properties and photovoltaic performance of the TiO 2 NPs-based thin films could be improved via thermal annealing.