| With the increasingly rapid economic growth, global demand for energy is-rising steadily. However, our natural resources are all limited and the traditional energy is becoming less and less, so, more attention has been paid to the development and utilization of new energy. Solar energy is an inexhaustible and environmental benign energy, over the past decades, which has attracted much attention in order to replace the environmentally damaging and diminishing fossil fuels. Up till now, traditional solar cells are made from silicon, due to easy, low cost and environmentally-friendly fabrication. Dye-sensitized solar cell (DSSC) is much cheaper than silicon solar cells. This technology provides a new approach for human to effectively utilize solar energy. TiO2photo-anode is the key component of DSSC which plays an important role in dye loading, electron injection, transportation and collection, etc. it can directly influence on the photoelectric performance of DSSC. Therefore, the development of a high-performance TiO2photo-anode module will become a hotspot in the research of DSSC.TiO2is a wide band-gap compound semiconductor with a direct band gap of3.2eV. The exploration of novel TiO2films has important significance to the development of semiconductor light-emitting materials, spintronics, photocatalysts, dye-sensitized solar cells, etc. TiO2nanocrystalline film is one of the electrode materials for DSSC, the most widely used and most studied, it is made of interconnected TiO2nano-particles with a three-dimensional network structure, which will guarantee the electronic transmission. On the other hand, the connection of TiO2nano-particles in the network structure is random and loose, so that will greatly affect the electron transport properties in the TiO2thin-film. TiO2nanotube arrays, a Ti metal surface preparation of dense and ordered nanoporous materials, its pipeline structure in the arrays can provide a high speed transmission channel for the photo-induced electrons, which will be beneficial for improving the mobility of electrons. Therefore, TiO2nanotube films have great value in the applications of DSSC and a wide developmental foreground. At present, the morphology of TiO2nanotubes are mostly line-shape, the related research mainly focused on the effective control of the nanotube length, diameter, wall thickness, and improving the quality of surface morphology of TiO2nanotube arrays, and so on. As the development of preparation methods and preparation process, the morphology of TiO2nanotubes is developing toward the multi-dimensional structure, such as two-(Y-branched), three-and two-generation Y-branched TiO2nanotube arrays. Based on the domestic and foreign development situation of dye-sensitized solar cells and the advantages of mature TiO2nanotubes fabrication technologies, our thesis is composed of the following contents:1. We discussed the important influence of two-step anodization method to the preparation of highly ordered TiO2nanotube arrays, and analysised of the mutual relations between the growth of TiO2nanotubes and experimental parameters. In the meantime, we also concluded a set of optimal technological parameters for the preparation of line-type TiO2nanotube arrays. All the results will lay a foundation for the design and preparation of Y-branched TiO2nanotube arrays.2. In order to develop the multidimensional structure of TiO2nanotube arrays, Y-branched TiO2nanotube arrays were fabricated on the Ti foil by electrochemical anodic oxidation via increasing the electrolyte temperature. We systematically studied the influence of electrolyte temperature on the morphology characteristics of the Y-branched TiO2nanotubes, and firstly introduced the growth mechanism of Y-branched TiO2nanotubes. Meanwhile, four samples were fabricated by anodic oxidation under different temperature ranges between20℃and60℃. As the results showed that the electrolyte temperature was set at40℃or more in the third step of anodic oxidation, the surface morphology of Y-branched TiO2nanotubes would appear annular nanowires, nanotube nozzle broken or stem nanotube length reduced, etc. That was not conducive to ensuring the overall quality of Y-branched TiO2nanotube arrays. Therefore,20℃～40℃would be the ideal temperature range in the third step during the anodizing process. In addition, we analyzed the effects of electrolyte temperature on the internal structure of Y-branched TiO2nanotubes, the result indicated that as the electrolyte temperature was increased, the V-shaped diameter structure of TiO2nanotubes would be enlarged, the Y-branched TiO2nanotube arrays could obtain a higher surface area.3. We successfully fabricated Y-branched TiO2nanotube arrays by a simplified two-step electrochemical anodic oxidation method via reducing the anodizing voltage. Compared to Y-branched TiO2nanotube arrays prepared by changing electrolyte temperature, this kind of samples have a better surface orderliness and higher occupancy of Y-branched nanotubes. At the meantime, we also illustrated here the synthesis process of Y-branched TiO2nanotubes by reducing the anodizing voltage and a possible growth mechanism. Moreover, to further expand the range of voltage reduction (34V-20V) and reduce the voltage for two times (38V-28V-20V), we obtained the three-branched TiO2nanotubes and two-generation Y-branched TiO2nanotubes, respectively.4. The assembly process of Y-branched TiO2nanotubes photo-anode was introduced here, and a series of different steps for assembly were discussed, such as solution detachment, white paper extraction, multi-step annealing and the preparation of nanocrystalline TiO2 slurry, etc. Then, we measured the photoelectric properties of DSSC assembled with Y-branched TiO2nanotubes, the open voltage, photocurrent density and conversion efficiency was evaluated. Compared to the DSSC assembled with line-shape TiO2nanotubes, we found that Y-branched TiO2nanotube DSSC showed more excellent photoelectric properties, the photoelectric conversion efficiency was increased from2.83%to3.35%, it was enhanced18.38%. |
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