Influence of the titanium pretreatment on the yield titania nanotube properties

Perovskite solar cells (PSCs) have attracted much research interest due to their advantageous photovoltaic performance. Their properties include for example high carrier mobility, wide optical absorption range, and high power conversion efficiency (PCE). In commonly used planar PSCs, the perovskite layer is sandwiched between the electron and hole transport layers (ETL and HTL). Usually, various inorganic metal oxides, such as TiO2, ZnO, and SnO2, are used as ETLs in PSCs. TiO2, the most studied ETL material, can be fabricated by various methods to produce the final titania layer with different shapes and morphology. For advantageous nanostructured titania, a simple and cheap preparation procedure, by electrochemical oxidation of Ti-foil or a Ti- film yields a high-quality dense array of vertically aligned titania nanotubes. Here we identified that the properties of the titanium substrate are important for the final properties of the ETL, and thus for the solar cell itself. In this work, the synthesis of TiO2 nanotubes by the anodization method is reported, as well as the influence of the (pre)treatment conditions on the resulting samples. We compare the TiO2 nanotubes prepared by electrochemical oxidation of titanium- foils and Ti-film generated by magnetron sputtering on glass substrates. The samples were prepared by pretreating the substrates in different atmospheres and at different temperatures, which provided better insight into the resulting shape and length of the prepared nanotubes, as well as their subsequent features. In the microscopy results we describe the morphology of the titania nanostructures obtained by anodization process. Different methods such as grazing incidence X-ray diffraction (GIXRD) and Kelvin probe force microscopy (KPFM) were employed for systematic characterization. Finally, the electrical properties of the samples were investigated using the solid-state impedance spectroscopy (SS-IS) method.