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Nanocrystalline TiO 2 thin films have been prepared by sol-gel dip coating method. The X-ray diffraction results showed that TiO 2 thin films annealed at 400, 450 and 500°C are of anatase phase and the peak corresponding to the (101) plane is present in all the samples. The grain size of TiO 2 thin films was found to increase with increasing annealing temperature. The grain size is found to be 20, 25 and 33 nm for the films annealed at 400, 450 and 500°C. The structure of the TiO 2 nanocrystalline thin films have been examined by high-resolution transmission electron microscope, Raman spectroscopy and FTIR spectroscopy. TiO 2 thin films were sensitized by natural dyes extracted from basella alba rubra spinach. It was found that the absorption peak of basella alba rubra extract is at about 665 nm. The dye-sensitized TiO 2-based solar cell sensitized using basella alba rubra exhibited a J sc of 4.35 mA cm-2 , V oc of 0.48 V, FF of 0.35 and efficiency of 0.70 %. Natural dyes as sensitizers for dye-sensitized solar cells are promising because of their environmental friendliness, low-cost production and fully biodegradable. Keywords Sol-gel Á TiO 2 nanocrystalline thin film Á Dye-sensitized solar cell

TiO 2 nanocrystalline thin films have various applications, among them dye-sensitized solar cells are more promising and low-cost alternative to conventional inorganic photovoltaic devices. TiO 2 nanocrystalline thin films have been sensitized with the natural dye (malvidin-3-fructoside) extracted from grape fruits. The interaction between the semiconductor and the dye has been studied. The maximum absorption band of grape extract at 525 nm has been shifted to 545 nm after incorporation of the dye indicating interaction of the dye molecules with TiO 2. The grape extract has polyphenolic anthocyanin pigment (malvidin-3-fructoside), which has carboxylic and hydroxyl groups that can attach effectively to the surface of TiO 2 film. The dye-sensitized TiO 2-based solar cell sensitized using grape dye exhibited a J sc of 4.06 mA/cm 2 , V oc of 0.43 V, FF of 0.33 and efficiency of 0.55 %. Natural dyesensitized TiO 2 photo electrodes present the prospect to be used as an environment-friendly, low-cost alternative system.

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