Abstract
The aim of this study is to investigate the potentials of TiO2 thin films for device applications. Nanocrystalline single phase of rutile TiO2 thin films have been prepared by Chemical Bath Deposition (CBD) technique at bath temperature range from 75-80C, keeping other deposition variables constant. The films were then subjected to post-deposition heat treatments with annealing temperatures in the range 373 to 673 K. The optical characterisation was done using the Elmer Lambda-2 spectrometer to investigate the transmittance and absorbance versus wavelength measurements. The data obtained from the transmittance and absorbance measurements were used to deduce the important optical constants. The results show that the energy bandgap was direct, with values in the range ≤1.8 eV for the as-deposited layers and ≥2.2 eV for the annealed layers. At lower temperatures, the band gaps of the annealed samples did not differ significantly from the energy gap (1.8 eV) of the as-deposited film. At higher thermal treatment, the energy gaps increased with the increase in annealing temperatures and a maximum of 2.2 eV for the energy gap was determined for TiO2 film annealed at 673 K. The values of the energy bandgap obtained in study, are within the range suitable for application in photovoltaic solar cell devices and in related photonic applications.
Highlights
The oxides of the transition metals have gained considerable attention recently
Reports by different research groups indicate that TiO2 thin films can be deposited using different deposition techniques inculding chemical bath deposition (CBD) method (Onah et al, 2013), Site-Selective Deposition (SSD) (Masuda, 2010), sputtering (Dakka et al, 1999) and metal-organic decomposition (Fukuda et al, 1999) etc
TiO2 thin films can be prepared in aqueous solutions at ordinary temperature
Summary
The oxides of the transition metals have gained considerable attention recently. One of such oxides is Titanium Oxide (TiO2). Deposition parameters of TiO2 thin films such as the substrate temperature, the complexing agents, concentration of the anionic and cationic precursors and deposition time could affect the structure of these films. These parameters have been proved to change the proportion of anatase (tetragonal) while rutile phase was thermodynamically stable (Fukuda et al, 1999; Viana et al, 2006). Crystalline titanium oxide thin films have been proved to increase in crystallinity and decrease in porosity as the thermal treatment temperature increased (Natarajan and Nogami, 1996)
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