Influence of a sputtered compact TiO2 layer on the properties of TiO2 nanotube photoanodes for solid-state DSSCs

- A sputtered TiO2 underlayer limits the side reaction of water oxidation during anodization, suppressing delamination issues of TiO2 nanotubes layers.
- The complete oxidation of titanium leads to an increased average transmittance in the visible from 65% to 74%.
- The electrical conductivity of the photoelectrodes with the underlayer is increased by an order of magnitude.
- The compact underlayer leads to an improved efficiency of these solid-state dye-sensitized solar cells, from 1.0% to 1.6%.

TiO2 nanotube arrays (TNA) elaborated on transparent and conducting substrates are promising materials for photoanodes in dye-sensitized solar cells as the reduced dimensionality enhances their transport properties. TNA were obtained by anodization of Ti films deposited by magnetron sputtering on transparent conducting oxide-coated glass. This study presents the impact of introducing a compact TiO2 underlayer on the morphological, optical and electrochemical properties of the TNA photoanodes.The TNA morphology was found to be more regular with a TiO2 underlayer and the macroscopic homogeneity of the samples was also increased. This is ascribed to a strong reduction, in the presence of the compact TiO2 underlayer, of a side reaction leading to oxygen evolution and destructuring the TNA film during anodization.As a consequence, the optical and transport properties (characterized by UV-vis and electrochemical impedance spectroscopy, respectively) were improved, together with an increased photovoltaic efficiency.

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