Abstract
Anodized TiO2 nanotubes have received much attention for their use in solar energy applications including water oxidation cells and hybrid solar cells [dye-sensitized solar cells (DSSCs) and bulk heterojuntion solar cells (BHJs)]. High surface area allows for increased dye-adsorption and photon absorption. Titania nanotubes grown by anodization of titanium in fluoride-containing electrolytes are aligned perpendicular to the substrate surface, reducing the electron diffusion path to the external circuit in solar cells. The nanotube morphology can be optimized for the various applications by adjusting the anodization parameters but the optimum crystallinity of the nanotube arrays remains to be realized. In addition to morphology and crystallinity, the method of device fabrication significantly affects photon and electron dynamics and its energy conversion efficiency. This paper provides the state-of-the-art knowledge to achieve experimental tailoring of morphological parameters including nanotube diameter, length, wall thickness, array surface smoothness, and annealing of nanotube arrays.
Highlights
Ordered TiO2 nanostructures, including nanoparticles, nanotubes, and nanorods [1,2] have garnered much research for their use in solar energy applications [3,4,5]
Titania nanotubes can be formed by other routes [10], the anodization method leads to an aligned array with an adjustable morphology that can be optimized for its various applications
Hybrid solar cells benefit from front-side illumination where light is incident on the transparent conducting oxide and immediately reaches the sensitized TiO2 nanotube array (Figure 12b,c) [31,48]
Summary
Ordered TiO2 nanostructures, including nanoparticles, nanotubes, and nanorods [1,2] have garnered much research for their use in solar energy applications [3,4,5]. The titania nanostructures accept electrons from photoexcited dye molecules or polymers adsorbed to the surface and direct the electrons into an external circuit. In photoelectrochemical cells for the degradation of pollutants or the oxidation of water, the photoexcited titania nanostructures donate electrons or holes to chemical species adsorbed to the surface. Titania nanotubes have attracted extensive research as photoanodes in hybrid solar cells, there are several complications that need to be overcome including phase separation between electron donors and titania, polymer penetration into the nanotubes, and efficient electrical contact with conductive glass [20,26]
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