Surface passivation of highly ordered TiO2 nanotube arrays and application to dye-sensitized solar cells using the concept of isoelectric point

Highly ordered TiO2 nanotube arrays have attracted much attention in an application to dye-sensitized solar cells (DSCs) due to their superior charge percolation. However, the efficiency of TiO2-nanotube-based DSCs is 6.89%, which is still lower than that of TiO2-nanoparticle-based DSCs. In this study, the surface passivation of highly ordered TiO2 nanotube arrays has been applied to increase the performance of TiO2-nanotube-based DSCs using the concept of isoelectric point. Both acidic oxide such as WO3 and basic oxides such as MgO, ZnO have been used as materials for surface passivation. The overall conversion efficiency of DSCs based on surface-passivated TiO2 nanotube arrays has been improved by these passivating layers.