Improved efficiency of betanin-based dye-sensitized solar cells

An improved separation technique employing medium pressure liquid chromatography is used to purify betanin from beet root for use as a sensitizer in a TiO2-based dye-sensitized solar cell. The use of a blocking layer and treatment by TiCl4 were explored in order to optimize the performance of the solar cell, resulting in energy conversion efficiencies as high as 2.7%, the highest yet recorded for a DSSC containing a single unmodified natural dye sensitizer. The fluorescence spectrum of betanin in aqueous solution is reported as a function of added colloidal TiO2, demonstrating efficient electron injection. Quenching of betanin fluorescence by TiO2 permits the observation of its resonance Raman spectrum, reported here for the first time and discussed in light of recent theoretical work on the electronic structure of betanin. We report the results of stability tests under continuous illumination and suggest ways to extend the lifetime of these solar cells.