Fabrication of nanocrystalline TiO2 thin films using Sol-Gel spin coating technology and investigation of its structural, morphology and optical characteristics

Although TiO2 is a popular semiconductor photocatalyst but due to its large bandgap (3.2 eV), its light absorption capability is limited to UV range (about 3 – 5% of solar spectrum), making it inefficient for solar energy conversion. However, light absorption capability can be increased by narrowing down the bandgap through a technique known as doping, but the dopants which are used in this process induces defect. These defect states present in the TiO2 lattice may act as recombination centres for the photogenerated charge carriers, thereby reducing the efficiency of solar energy conversion. As a result, defects from the doping are the limitation towards increasing the efficiency of TiO2 for solar energy conversion. So, researchers have been searching for a dopant free technique to narrow down bandgap of anatase TiO2 below 3.2 eV. This paper demonstrates a new cost-effective technique called as Sol-Gel employing spin coating technology for the fabrication of nanocrystalline TiO2 thin films. Following that, freshly formed TiO2 thin film samples were annealed at temperatures ranging from 400 °C to 550 °C and a thorough investigation on their structures, optical characteristics and surface morphology, were analysed using X-Ray diffraction, Raman spectroscopy, UV–Vis spectroscopy, FESEM and AFM etc. and are presented in this paper. Unlike any other previously performed sol–gel method, we have managed to achieve dopant free purely anatase nanocrystalline TiO2 thin film with low band gap reaching up to 2.68 eV.