Anodically grown TiO2 nanotube membranes: Synthesis, characterization, and application in dye-sensitized solar cells

Abstract

First proposed more than 20 years ago, dye-sensitized solar cells represent one of the most interesting non-silicon solar harvesters, with outstanding potential as low-cost devices wiTheasy fabrication process. Their standard architecture is constituted by a dye-sensitized TiO2 nanoparticle-based photoanode, a hole-conducting liquid electrolyte and a platinized counter electrode. Even if nanoparticles offer a high number of sites for dye molecule chemisorption, they exhibit limited transport and recombination properties with respect to 1D nanostructures such as nanowires or nanotubes. In view of increasing the dye-sensitized solar cell conversion efficiency, new one-dimensional metal-oxide nanostructures are suggested to be employed as photoanodes. In this chapter the fabrication and characterization of free-standing TiO2 nanotube membranes and their integration in front-side illuminated dye-sensitized solar cells are reported. Vertically oriented TiO2 nanotube arrays are fabricated by anodic oxidation, a simple electrochemical technique. The charge transport and recombination mechanisms in the oxide nanostructures are studied by electrochemical impedance spectroscopy. The first part of the chapter is devoted to describe the dye-sensitized solar cell working principles, the anodic oxidation process, and the electrochemical impedance spectroscopy measurements. In the second part the TiO2 nanotube membrane fabrication and the results obtained on dye-sensitized solar cells are presented, showing the effectiveness of the use of 1D nanostructures as photoanode materials.