Abstract
Increase in world population has led to more energy demand. Therefore, there is need for utilization of green and renewable energy. Dye sensitized solar cells (DSSCs) based on TiO<sub>2</sub> have attracted a lot of attention as an alternative source as compared to current silicon technology. In this study, TiO<sub>2</sub> thin films were deposited on doped fluorine tin oxide layer (FTO) glass substrates using sol-gel doctor blading technique. The films were annealed at different rates (1step, 2°C/min and 1°C/min) up to a temperature of 450°C followed by sintering at this temperature for 30 minutes. UV-VIS spectrophotometry was employed to probe the absorbance and reflectance of the films. It was found that, the optical parameters, such as the reflectance, the real (ε<sub>1</sub>) and imaginary (ε<sub>2</sub>) parts of dielectric constant, skin depth, Urbach energy and the energy gap; all depend on the annealing rate. The skin depth for the samples in visible region were found to increase from 6.319 x 10<sup>-5</sup> to 11.968 x 10<sup>-5</sup> cm<sup>-1</sup> due to annealing. The Optical band energy (Eg) decreased from 5.04eV for as deposited film to 4.35eV at annealing rate of 1°C/min for direct allowed and from 2.76 to 2.56 eV for indirect transitions. Urbach tails in weak absorption region decreased with annealing rate. Urbach energies (Eu) were in the range of 432-505 meV for as deposited and annealed films. This was used to account for the disorder of the films. An inverse relation between Urbach energy and optical band energy as result of annealing rate was reported.
Highlights
Titanium IV oxide (TiO2) in the recent decades is attracting much attention to many researchers due to its excellent chemical, thermal, optical and electrical properties
The surface morphology is strongly affected by the annealing temperatures of TiO2 thin films
TiO2 thin films were deposited on fluorine tin oxide layer (FTO) (SnO2: F) 7 Ω/sq
Summary
Titanium IV oxide (TiO2) in the recent decades is attracting much attention to many researchers due to its excellent chemical, thermal, optical and electrical properties. TiO2 in nature occurs in the structure of anatase, rutile and brookite [7]. The layer thickness of TiO2 decreases with increase in annealing temperature attributed to densification of the titanium dioxide layer and evaporation of the carbonaceous material and absorbed water [9]. The highest refractive index obtained for anatase TiO2 is 2.26 which increases to 2.57 with further annealing. This can be explained by crystalline structure development [10]. UV-VIS studies on optical absorption properties of TiO2 has shown sharp absorption edges in the UV region and the absorption varying with annealing temperature. The absorption edge (in anatase) annealed at 450°C showed a red shift into the visible region [11]. The UV absorption peaks in American Journal of Nanosciences 2021; 7(1): 28-34
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