Layered γ-zirconium phosphate as novel semiconductor for dye sensitized solar cells: Improvement of photovoltaic efficiency by intercalation of a ruthenium complex-viologen dyad

The performance of photovoltaic cells using as semiconductor a film of layered gamma-zirconium phosphate (gamma-ZrP) containing Ru(bpy)(3) and bipyridinium ions (viologens) as electron relays has been studied. The materials are easily prepared by intercalation of Ru complexes and the bipyridinium ions into preformed gamma-ZrP nano sheets as colloidal solutions in the appropriate solvent and concentration. High loading of these two guests has been obtained as determined by elemental analysis. Inclusion of Ru (bpy)(3) complex and bipyridinium in the intergallery spaces of gamma-ZrP can be assessed by powder XRD monitoring of the d(100) peak. A dyad was also synthesized where the Ru(bpy)(3) and the 4,4'-bipyridinium were covalently connected by a four-methylene tether. The semiconducting behavior of layered gamma-ZrP was supported by cyclic voltammetry (reversible reduction peak at -0.6 V), observation of photocurrent and Mott-Schottky measurements (flat band potential similar to-1.3 V vs. NHE) of thin films of this material supported on FTO electrode. Photovoltaic cells based on gamma-ZrP containing Ru(bpy)(3), exhibited similar V(OC) (similar to 0.5 V) and fill-factor values (0.3-0.4), differing in the current density and therefore in their efficiency. The maximum efficiency was obtained for the material containing high loading of the dyad (J(SC) = 0.383 mA/cm(2), efficiency 0.1%). The photo response spectrum shows that the main limitation of these materials is still the inefficient photo sensitization of the semiconductor by the dye, probably due to the high negative flat band potential of gamma-ZrP.