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 75-80C, 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.

Keywords:

Energy band gap, solar cells, TiO₂, thermal annealing,

References

1. Bozorgtabar, M., M. Rahimipour, M. Salehi and M. Jafarpour, 2011a. The photo-absorption and surface feature of nanostructured TiO2 coatings. World Acad. Sci. Eng. Technol., 56: 346-350.
   Direct Link
2. Bozorgtabar, M., M. Rahimipour, M. Salehi and M. Jafarpour, 2011b. The photo-absorption and surface feature of nano-structured TIO2 coatings. Int. J. Chem. Mol. Nucl. Mater. Metallur. Eng., 5(8): 652-654.
   
3. Dakka, A., J. Lafait, M. Abd-Lefdil and C. Sella, 1999. Optical study of titanium dioxide thin films prepared by R.F. sputtering. MJ Cond. Matt., 2(1): 153-156.
   
4. Deshpande, N.G., J.C. Vyas and R. Sharma, 2008. Preparation and characterization of nanocrystalline tin oxide thin films deposited at room temperature. Thin Solid Films, 516(23): 8587-8593.
   CrossRef    Direct Link
5. Eufinger, K., D. Poelman, H. Poelman, R. De Gryse and G.B. Marin, 2008. Ti02 thin films for photocatalytic applications. Thin Solid Films Process Appl., 37(661): 189-227.
   
6. Fukuda, H., Y. Ishikawa, S. Namioka and S. Nomura, 1999. Synthesis of high-K titanium oxide thin films formed by metalorganic decomposition. MRS Proc., 606: 163.
   
7. Masuda, Y., 2010. Morphology Control, Self-assembly and Site-selective Deposition of Nanocrystals. INTECH Open Access Publisher.
   
8. Mordi, C.U., M.A. Eleruja, B.A. Taleatu, G.O. Egharevba, A.V. Adedeji, O.O. Akinwunmi, B. Olofinjana, C. Jeynes and E.O.B. Ajayi, 2009. Metal organic chemical vapour deposited thin films of cobalt oxide prepared via cobalt acetylacetonate. J. Mater. Sci. Technol., 25(1): 85-89.
   Direct Link
9. Natarajan, C. and G. Nogami, 1996. Cathodic electrodeposition of nanocrystalline titanium dioxide thin films. J. Electrochem. Soc., 143(5): 1547-1550.
   CrossRef    Direct Link
10. Nwofe, P.A., K.T. Ramakrishna Reddy, J.K. Tan, I. Forbes and R.W. Miles, 2013a. On the structural and optical properties of SnS films grown by thermal evaporation method. J. Phys. Conf. Ser., 417(1): 012039.
    CrossRef    Direct Link
11. Nwofe, P.A., R.W. Miles and K.T. Ramakrishna Reddy, 2013b. Effects of sulphur and air annealing on the properties of thermally evaporated SnS layers for application in thin film solar cell devices. J. Renew. Sust. Energ., 5(1): 011204.
    CrossRef    Direct Link
12. Onah, D.U., J.E. Ekpe, M.A. Elebe and E. Nnaji, 2013. Optical characterization of chemical bath deposited nanocrystalline TiO thin films. J. Niger. Assoc. Math. Phys., 24: 361-364.
    Direct Link
13. Pankove, J.I., 1985. Optical Processes in Semiconductors. Prentice-Hall Inc., New Jersey.
    
14. Pathan, H.M., W.Y. Kim, K.D. Jung and O.S. Joo, 2005. A chemical route to room-temperature synthesis of nanocrystalline TiO2 thin films. Appl. Surf. Sci., 246(1-3): 72-76.
    CrossRef    Direct Link
15. Ritter, E. 1975. Dielectric film materials for optical applications. Phys. Thin Films, 8: 1-49.
    
16. Ubale, A.U., R.J. Dhokne, P.S. Chikhlikar, V.S. Sangawar and D.K. Kulkarni, 2006. Characterization of nanocrystalline cadmium telluride thin films grown by successive ionic layer adsorption and reaction (SILAR) method. B. Mater. Sci., 29(2): 165-168.
    
17. Viana, M.M., T.D.S. Mohallem, G.L.T. Nascimento and N.D.S. Mohallem, 2006. Nanocrystalline titanium oxide thin films prepared by sol-gel process. Braz. J. Phys., 36(3B): 1081-1083.
    CrossRef    Direct Link

Competing interests

The authors have no competing interests.

Open Access Policy

This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Copyright

The authors have no competing interests.