Photovoltaic Performance of Spherical TiO2 Nanoparticles Derived from Titanium Hydroxide Ti(OH)4: Role of Annealing Varying Temperature

Abstract

High-quality titanium dioxide (TiO2 or titania) nanoparticles (TiO2 NPs) with tailored morphologies are desirable for efficient photovoltaic applications. In this view, some thin films containing spherical TiO2 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 TiO2 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 TiO2 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 TiO2 NPs-based thin films could be improved via thermal annealing.