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

Tin oxide (SnO 2 ) 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 SnO 2 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 SnO 2 nanotube arrays may be feasibly synthesized through a liquid-phase conversion process, and the synthesized SnO 2 nanotubes can be further coated with a thin layer of TiO 2 to form hybrid TiO 2 –SnO 2 nanotube arrays. Both the resulting SnO 2 and hybrid TiO 2 –SnO 2 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 TiO 2 –SnO 2 nanotubes is significantly larger than those in TiO 2 nanotubes, ZnO nanowires, and films of sintered TiO 2 nanoparticles, suggesting promise of the TiO 2 -coated SnO 2 nanotubes for further improvement of DSCs.