Hybrid TiO2–SnO2 Nanotube Arrays for Dye-Sensitized Solar Cells

Tin oxide (SnO2) is a promising wide band gap semiconductor material for dye-sensitized solar cells (DSCs) because of its high bulk electron mobility. Employing vertically ordered 1-D nanostructures of SnO2 as the photoanode may overcome the limit of current DSCs by using new redox mediators with faster kinetics than currently used ones. Synthesizing such nanostructures and integrating them into DSCs, however, has been proven challenging. Here, we demonstrate that, by using ZnO nanowires as a sacrificial template, vertically aligned SnO2 nanotube arrays may be feasibly synthesized through a liquid-phase conversion process, and the synthesized SnO2 nanotubes can be further coated with a thin layer of TiO2 to form hybrid TiO2–SnO2 nanotube arrays. Both the resulting SnO2 and hybrid TiO2–SnO2 nanotube arrays are used to fabricate DSCs, and the best performing cell delivers a promising efficiency of 3.53%. Transient photovoltage measurements indicate that the electron recombination lifetime in hybrid TiO2–SnO2 nanotubes is significantly larger than those in TiO2 nanotubes, ZnO nanowires, and films of sintered TiO2 nanoparticles, suggesting promise of the TiO2-coated SnO2 nanotubes for further improvement of DSCs.