All-Plastic Flexible Dye-Sensitized Solar Cell Based on Solution Synthesized Mesoporous Anatase TiO₂Beads

Abstract

Synthesis of mesoporous anatase TiO 2 beads via a simple two-step solution process without an additional calcination step is reported. The method involves a sol-gel and a hydrothermal techniques. Hexamine was used as the steric agent during the sol-gel process for the formation of the beads with controllable sizes. Also, the high water solubility of hexamine allows its easy removal, thus eliminating the existence of organic residue in the subsequent steps and the final product. The resulting beads were characterized using X-ray diffraction, high resolution scanning and transmission electron microscopy, X-ray absorption near edge structure analysis, and X-ray photoelectron spectroscopy. The beads were made into photoanodes with and without the addition of commercial TiO 2 powders. We show an obvious efficiency enhancement in the resulting all-plastic flexible dye-sensitized solar cell, demonstrating that the obtained mesoporous anatase TiO 2 beads with well-defined characteristics are an excellent candidate for energy applications.Synthesis of TiO 2 materials with controlled, well-defined structures such as single crystals, 1 nanowires, 2 nanotubes, 3 ordered mesoporous films, 4 and spherical particles, 5,6 is of great interest. Especially, spherical TiO 2 particles have found themselves various applications in different environmental and energy-related fields. One of the important applications is related to dye-sensitized solar cell (DSC). 5-10 So far, various methods for making spherical TiO 2 particles have been developed. Examples include a variety of hydrothermal processes 5,6,8 and template-assisted synthesis. 11,12 For use in DSC, the TiO 2 particles are required to exhibit high a specific surface area and phase purity. As a result, recent efforts have been directed to the synthesis of micro-sized mesopores TiO 2 beads which, however, is still at the infant stage. 13 In this study, we report the synthesis of such mesoporous anatase TiO 2 beads with various sizes and characteristics via a simple two-step solution method involving a sol-gel and a hydrothermal techniques. Such an approach was inspired by the work of Chen et al. 5,14 However, the method does not require an additional calcination step. In the meantime, we have used hexamine during the sol-gel process. The non-ionic tertiary amine attached on nanoparticles serve as a steric agent. The hexamine surrounds the O-Ti-O clusters such that individual clusters can be separated, hence functioning as a steric agent. Therefore, depending in the amount of the hexamine sol-gel particles, and hence beads, having controlable sizes can be obtained. Due to its high water solubility, hexamine can be easily removed by water, thus eliminating the organic residues that often occur in the follow-up steps and the final product. Also, hexamine's tertiary-amine structure makes the steric effect more efficient, resulting the minimal use of steric agent. Moreover, we also show an obvious efficiency enhancement in plastic substrate flexible DSC (FDSC) due to the use of the ...

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