Hydrothermal growth of Bi2Ti2O7/TiO2 and Bi4Ti3O12/TiO2 heterostructures on highly ordered TiO2-nanotube arrays for dye-sensitized solar cells

Secure solar energy has been considered to be a possible way to alleviate the energy crisis. Using a hydrothermal reaction, functional heterostructures, including Bi2Ti2O7 and Bi4Ti3O12, were assembled on highly ordered TiO2-nanotube arrays that were prepared via a two-step anodic-oxidation method. The loading of the heterostructure onto the arrays was controlled by adapting the reaction temperature and alkalinity of the hydrothermal reaction. The samples were assembled into dye-sensitive solar cells to study their photoelectric performance. The optimal photoelectric-conversion efficiencies of Bi4Ti3O12/TiO2 (synthesized at 200 degrees C and pH 13.7) were 2.3 times greater than those of pure TiO2-nanotube arrays. The photoelectric property was enhanced due to the increase in the photoabsorption that originated from the introduction of the dyes, as well as the improvement in the charge-separation efficiency, which was derived from the matching of the energy-bands between the bismuth titanate and TiO2. The ferroelectric properties of Bi4Ti3O12 also played an important role in the enhanced photoelectric property.