Dye-sensitized sputtered titanium oxide films for photovoltaic applications: influence of the O2/Ar gas flow ratio during the deposition

Titanium oxide films were prepared by reactive DC magnetron sputtering onto SnO2:F coated glass substrates. The O2/Ar gas flow ratio was kept at a constant value Γ during the deposition, and a series of films were deposited with 0.050<Γ<0.072. Structural studies were performed by X-ray diffraction and transmission electron microscopy; the structure displayed penniform features with a clear dependence on Γ. Charge transport in the films was evaluated by use of time-resolved photocurrents; a diffusion model was fitted to the experimental data and two different transport mechanisms were proposed depending on the film stoichiometry. Dye sensitization in cis-dithiocyanato-bis(2,2′-bipyridyl-4,4′-dicarboxylate) ruthenium (II) was performed to evaluate incident photon-to-current conversion efficiency and solar cell properties of the films. These parameters showed a clear dependence on Γ. Optical measurements gave evidence for the presence of polaron absorption for the film deposited at Γ=0.050.