| nanomaterials have been extensively studied for applications like self-cleaning, dielectric materials, sensors, photocatalyst and dye-sensitized solar cells due to its advantages in rich resources, nontoxicity, and high chemical stability. In recent years, TiO2 nanotubes and nanowires have been applied in dye-sensitized solar cells and photocatalysts. In this work, a series of TiO2 nanotube arrays with well-controlled morphologies were prepared by different methods. The applications of the prepared TiO2 nanomaterials in solar cells were exploited, and the relationship between the structure and their photo-electronic properties was studied.The main results are listed below:1. A novel coaxial TiO2/ZnO nanotube array has been prepared by electrochemical deposition of ZnO into highly ordered TiO2 nanotubes array. The TiO2/ZnO nanotube arrays can be applied as an efficient photoanode in dye-sensitized solar cells (DSSCs). Such photoanode benefits from the capability of high sensitizer loading offered by the high specific surface and the direct conduction path for electrons through the nanotubes. With the coaxial TiO2/ZnO nanotubes as the photoanode, DSSCs with an overall 2.8% energy-conversion efficiency was obtained, which was a 40% improvement over the DSSC that uses pure TiO2 nanotubes as photoanode.2. Highly uniform TiO2 nanotube arrays with regular periodical sidewall morphology were fabricated by both alternating-voltage (AV) anodization and alternating-current (AC) anodization methods. The periodical morphology exhibited obvious decay under AV condition, and the tubes became smooth after certain length. In contrast, the tube morphology showed much stronger correlation with the wave-function of the driving current under the AC condition. Dye-sensitized solar cells were fabricated with the different TiO2 nanotube arrays, and the effects of different wall morphologies on the cell performance were investigated. It was found that the tube arrays fabricated by the AC method with square-wave driving current give the highest efficiency, which reached 3.47%.3. Dye-sensitized solar cells were prepared with TiO2 nanoparticles on TiO2 nanotube arrays by electrophoretic deposition method. A slow electron recombination and a light scattering effect might have simultaneously contributed to the DSSCs performance and resulted in improvements in the short-circuit current (Jsc) and the conversion efficiency. The TiO2 nanoparticles on TiO2 nanotubes increased the electrode surface area and the dye adsorption, while the TiO2 nanotubes improved the performance of the charge collection and transmission. The combination of these features leads to improved light absorption, electron photogeneration, and charge collection effects. It is concluded that the improvement of total effective for the multilayer composite film benefits from the combined utilization of effective light-scattering and high-efficiency electron transport.4. We have successfully prepared TiO2 nanorod arrays on FTO substrate by hydrothermal method. The TiO2 nanorod array is sequentially modified by CdS, CdSe quantum dots using a chemical bath deposition method. The co-sensitized electrod exhibited significantly improved photo response, including both expanded spectral response range and decreased electron-hole recombination rate. The decreased electron-hole recombination rate results in the decrease of electron transport resistance and the improvement of electron transport efficiency, and accordingly the improvement of power convertion efficiency and photocatalytic efficiency.5. We present a solid-state solar cell design, consisting of vertically aligned TiO2 nanotubes arrays. The arrays were sensitied by CdS and CdSe quantum dots and were uniformly infiltrated with p-type poly(3-hexylthiophene-2,5-diyl) (P3HT). The quantum dots absorb the visible light while the P3HT absorbs higher energy photons. Our solid-state solar cells exhibit broad spectral response with monochromatic incident photon-to-electron conversion efficiency (IPCE) yields up to 13%. The power conversion efficiency of these TiO2 nanotubes/CdS/CdSe/P3HT solid-state hybrid solar cells was also improved.
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