Enhanced Charge-Collection Efficiencies and Light Scattering in Dye-Sensitized Solar Cells Using Oriented TiO₂ Nanotubes Arrays

TLDR

The study investigates electron transport and recombination dynamics in dye‑sensitized solar cells using oriented TiO₂ nanotube arrays. The authors fabricated TiO₂ nanotube arrays by electrochemical anodization of Ti foils, characterized their morphology with electron microscopy, and examined their transport and recombination behavior in DSSCs using frequency‑resolved modulated photocurrent/photovoltage spectroscopy. The densely packed, micrometer‑long, fully crystalline nanotube arrays exhibit comparable transport times but significantly slower recombination, resulting in higher charge‑collection and light‑harvesting efficiencies than nanoparticle‑based cells, partly due to stronger internal light‑scattering and complete dye coverage of the tube walls.

Abstract

We report on the microstructure and dynamics of electron transport and recombination in dye-sensitized solar cells (DSSCs) incorporating oriented TiO2 nanotube (NT) arrays. The morphology of the NT arrays, which were prepared from electrochemically anodized Ti foils, were characterized by scanning and transmission electron microscopies. The arrays were found to consist of closely packed NTs, several micrometers in length, with typical wall thicknesses and intertube spacings of 8-10 nm and pore diameters of about 30 nm. The calcined material was fully crystalline with individual NTs consisting of about 30 nm sized crystallites. The transport and recombination properties of the NT and nanoparticle (NP) films used in DSSCs were studied by frequency-resolved modulated photocurrent/photovoltage spectroscopies. While both morphologies display comparable transport times, recombination was much slower in the NT films, indicating that the NT-based DSSCs have significantly higher charge-collection efficiencies than their NP-based counterparts. Dye molecules were shown to cover both the interior and exterior walls of the NTs. Analysis of photocurrent measurements indicates that the light-harvesting efficiencies of NT-based DSSCs were higher than those found for DSSCs incorporating NPs owing to stronger internal light-scattering effects.