| Vertical oriented highly ordered TiO2nanotube arrays (TNAs) represent extrodinary electron transport and photochemical properties due to their unique vertical aligned geomitric structure. And TNAs show a great potential in the application of quantum-dot-sensitized solar cells (QDSSCs). Moreover, it can be also camparable to the nano porous TiO2. At present, however, there are many proplems in QDSSCs for their widespread applications, such as weak absorption of CdS quantum dots (QDs) in the surface of TNAs, existing surface states in TNAs which are easy to form recombination centers, the interface proplem between CdS QDs and TNAs, electrolyte that can not completely fill into the nanotubes for reaction in the cells and so on. Thereinto, the majoy proplems are surface states and interface between semiconductor materials and sensitizer. In this paper, we modify the surface of TNAs through the mothod of surface modification to decrease the surface tension and states. After modification, CdS QDs uniformly distributed on the TNAs represent an improvement in tansport performance and conversion efficiency.The photoelectrical properties of highly ordered TNAs have been systematically and quantitatively studied and found to be closely related to their geometric and crystal structures. The geometric characteristics, including the nanotube diameter and length, were modified by adjusting the anodization potentials and durations, while the crystal structure was modified by thermal annealing at different temperatures. Under the same voltage and the same time, the nanotube array samples with the mixed crystalline phases possess higher photoconversion efficiency than those with the single anatase or rutile phase. The optimal content of rutile phase is about twice of that of anatase phase. In terms of the influence of the geometric structure, under the same annealing temperature, the TNAs with larger inner diameters and longer tube lengths have better photoelectrical properties. Besides, in order to further observe the photochemical properties of the TNAs, a geometric roughness factor has been applied to describe the combinative effect of the geometric characteristics for the propertes of TNAs. The TNAs with the geometric roughness factor of125.32shows the superior photoconversion efficiency of13.2%.TNAs were made using anodic oxidation, and then the samples were deposited the CdS QDs to prepare the quantum dot-snesitized solar cells. Accordingly, we can obtain the optimal preparation conditions. Under the same oxidation voltage, annealing temperature and deposition cycles, the solar cells have a better conversion efficiency of0.15%when the sample was anodized for4h. Similarly, under the same oxidation voltage, oxidation time and deposition cycles, the solar cells have a better conversion efficiency of0.15%when the sample was annealed at450℃. And the cells have a better conversion efficiency of0.15%when the sample was deposited CdS QDs for4cycles.Similarly, CdS QDs sensitized TNAs have been fabricated using the method of successive ionic layer adsorption and reaction and used as a photoanode for quantum dot-sensitized solar cells. Before coated with CdS, the surface of TNAs were treated with TiO2, nitric acid (HNO3), potassium hydroxide (KOH) and methyltrimethoxysilane (MTMS), respectively, for the purpose of reducing the interface transfer resistance of quantum-dot-sensitized solar cells. The surfaces of the modified samples represent the characteristics of super-hydrophilic and hydrophobic which directly affect the conversion efficiency of the solar cells. The results show that surface modification resulted in the change of the surface tension, which played a significant role in the connectivity of CdS and TNAs. In addition, the solar cell based on CdS/TNAs electrode treated by HNO3achieves a maximum conversion efficiency of0.17%, which is42%higher than that of the reference sample without any modification. |
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