High efficiency dye-sensitized solar cells based on hierarchically structured nanotubes

Dye-sensitized solar cells (DSSCs) based on hierarchically structured TiO₂ nanotubes prepared by a facile combination of two-step electrochemical anodization with a hydrothermal process exhibited remarkable performance. Vertically oriented, smooth TiO₂ nanotube arrays fabricated by a two-step anodic oxidation were subjected to hydrothermal treatment, thereby creating advantageous roughness on the TiO₂ nanotube surface (i.e., forming hierarchically structured nanotube arrays-nanoscopic tubes composed of a large number of nanoparticles on the surface) that led to an increased dye loading. Subsequently, these nanotubes were exploited to produce DSSCs in a backside illumination mode, yielding a significantly high power conversion efficiency, of 7.12%, which was further increased to 7.75% upon exposure to O₂ plasma.