Effect of Heat-Treatment on Electron Transport Process in TiO[sub 2] Nanotube Arrays Prepared Through Liquid Phase Deposition for Dye-Sensitized Solar Cells

Abstract

Nanotube arrays of TiO 2 were synthesized by using a template of ZnO nanorod arrays on fluorine-doped SnO 2 transparent conducting oxide glass substrate by liquid phase deposition method. Dye N719-sensitized photoelectrochemical cells comprising TiO 2 nanotube arrays were fabricated and characterized. With an increase in the calcination temperature, the anatase content of the crystallized film increased and the conduction band of TiO 2 shifted toward a negative potential, resulting in an increase in the cell performance in terms of the short-circuit photocurrent density and open-circuit voltage.The solar cell is one of the most promising tools for the utilization of solar power as renewable energy because it has the potential for solving environmental problems and insufficient energy problems. Since O'Regan and Grätzel reported on dye-sensitized solar cells ͑DSCs͒ based on a nanocrystalline porous TiO 2 electrode in 1991, 1 DSCs were studied as a type of solar cell and were expected to be a low cost alternative to conventional solid-state devices. The cells consist of a dye-adsorbed mesoporous metal-oxide film filled with an iodide/tri-iodide redox electrolyte and a Pt counter electrode. The mesoporous metal-oxide film, typically constructed using a thick film ͑ϳ10 m͒ of TiO 2 or, less often, SnO 2 or ZnO nanoparticles with a large surface area, plays a crucial role in the high performance of DSCs. 2-4 Such nanoparticles of metal oxide not only adsorb many dye molecules for efficient light harvesting but also serve as a semiconductor to provide a pathway for electron percolation through the film. The slow percolation of electrons through an amorphous network is one of the major factors limiting further improvement in the photoconversion efficiencies achievable with nanocrystalline DSCs. 5 The arrangement of the ordered titania nanotube array attached perpendicular to the surface permits facile charge transfer along the length of the nanotubes from the solution to the conductive substrate, thereby reducing the losses incurred by charge hopping across the nanoparticle grain boundaries. 6 Easier access to the nanotube array surface, as well as better control of the interface, makes this morphology desirable for DSCs. 5-8 Recently, Shankar et al. applied high ordered TiO 2 nanotube arrays made by the anodization of a titanium film sensitized with a donor-antenna dye to DSCs and achieved 6.1% photon-to-current conversion efficiency. 9 Titania nanotubes and nanotube arrays have been produced by a variety of methods including deposition into a nanoporous alumina template, 9-12 sol-gel transcription using organogelators as templates, 13,14 seeded growth, 15 and hydrothermal processes. [16][17][18] Of these nanotube fabrication routes, the architecture demonstrating by far the most remarkable properties are highly ordered nanotube arrays made by the anodization of titanium in fluoride-based baths, 19-25 the dimensions of which can be precisely controlled. However, DSCs fabricated with titania nanotube arrays made by anodi...

Branched TiO2 Nanorod Arrays Coated by TiO2 Nanosheets for Dye Sensitized Solar Cells

“…Preparation of highly ordered one-dimensional(1-D) nanomaterials and their application in dye-sensitized solar cells(DSSCs) have attracted a wide attention. The traditional techniques including template method and hydrothermal method have their own advantages and disadvantages [1][2][3] . In this work, the branched mixed crystal TiO 2 nanorod arrays have been developed on FTO for DSSCs by incorporating ZnO template and hydrothermal method.…”