Development of dye-sensitized solar cells based on visible-light-responsive TiO2 thin films with a unique columnar structure

A visible-light-responsive TiO2 thin film (Vis-TiO2), possessing a unique columnar structure oriented perpendicular to the substrate, has been prepared by using a radio-frequency magnetron sputtering deposition method. The unique TiO2 thin film was used as a key component of N719 dye-sensitized solar cells (DSSCs). The rough morphology caused by the columnar structure leads to enhanced photovoltaic performances of these DSSCs as a consequence of increased amounts of adsorbed dyes and facilitated diffusion of the electrolyte into Vis-TiO2 film. Additionally, photovoltaic performances of the DSSCs were found to depend strongly on the thickness of the Vis-TiO2 film, which can be readily controlled by adjusting the sputtering time conducted for deposition. Consequently, a solar-to-electric energy conversion efficiency of 2.6 % under AM 1.5 illumination was observed for an optimally performing DSSC that has a Vis-TiO2 film thickness of 6.9 mu m, prepared by employing a sputtering time of 700 min.