Evolution of structural and optical properties of rutile TiO2 thin films synthesized at room temperature by chemical bath deposition method

• Nanocrystalline rutile TiO2 was synthesized at room temperature.
• Rutile TiO2 synthesis was confirmed by low-angle XRD and Raman and FTIR spectroscopy.
• Rutile TiO2 films show a high absorption coefficient and a direct bandgap.
• The material is useful for the fabrication of extremely thin absorber and dye-sensitized solar cells.

Nanocrystalline thin films of TiO2 were prepared on glass substrates from an aqueous solution of TiCl3 and NH4OH at room temperature using the simple and cost-effective chemical bath deposition (CBD) method. The influence of deposition time on structural, morphological and optical properties was systematically investigated. TiO2 transition from a mixed anatase–rutile phase to a pure rutile phase was revealed by low-angle XRD and Raman spectroscopy. Rutile phase formation was confirmed by FTIR spectroscopy. Scanning electron micrographs revealed that the multigrain structure of as-deposited TiO2 thin films was completely converted into semi-spherical nanoparticles. Optical studies showed that rutile thin films had a high absorption coefficient and a direct bandgap. The optical bandgap decreased slightly (3.29–3.07 eV) with increasing deposition time. The ease of deposition of rutile thin films at low temperature is useful for the fabrication of extremely thin absorber (ETA) solar cells, dye-sensitized solar cells, and gas sensors.