Single Crystalline-like and Nanostructured TiO2 Photoanodes for Dye Sensitized Solar Cells Synthesized by Reactive Magnetron Sputtering at Glancing Angle

The control of the surface area enhancement and the ordering of the mesoporous photoanode is one of the key parameters to overcome the current limits of performance of dye sensitized solar cells (DSSCs). These parameters are expected to improve both the concentration of adsorbed dye molecules on the photoanode and the charge collection. In this paper, reactive magnetron sputtering at glancing angle is employed to synthesize nanostructured TiO2 thin films. A post-annealing treatment under an ambient atmosphere at 773 K allows recrystallization of the films to form individual single crystal-like anatase nanocolumns, as shown on a reference structure constituted by well-separated slanted nanocolumns. Even if the best cells provide an open circuit voltage of 0.8 V, a fill factor of 77%, and a short circuit current density of 4.6 mA/cm2 (JSC) and permit to reach an overall efficiency up to 2.6%, it does not yet reach the performances of the reference TiO2 nanoparticle (NP)-based cell. This is explained by a poor carrier collection efficiency, as demonstrated by intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy. The evaluation of other nanostructures such as zigzag and pillars shows the superiority of these structures on the NPs in terms of charge carrier collection efficiency. Nevertheless, the low penetration of the dye on these structures does not allow them to reach photovoltaic performances as good as those measured in NP-based DSSCs.