| Owing to its characteristics of being remarkably optical, electrical, magnetic, inexpensive, non-toxic and high active, etc., two family members of one-dimensional arrays of semiconductor nanostructures (one-dimensional ZnO and TiO2), are not only the focus of attention in the research areas of energy conversion, photovoltaic cells, lithium batteries and photocatalytic degradation of pollutants, etc., but also they have the potential applications in the fields of electrochromic, electroluminescent displays, microelectronic devices, sensors and absorbing and other fields. However, according to the relative literature, the preparations of ZnO and TiO2 nanostructure arrays with controllable shape, orientation, surface area, size and density are mostly conducted under the conditions with harsh experimental conditions and process requirements, and most of them could only be synthesized into smaller nano-arrays. Thus, the future research topics focus on the following three aspects:â‘ looking for simple, convenient and low-power preparation process to synthesize one-dimensional arrays of nanostructure with better structure and larger surface area;â‘¡studying their growth mechanism and the performances in their photoelectric conversion, photovoltaic cells and electro chromic field, etc.;â‘¢building ideal electrodes with their development and applications.In this paper, we report for the first time the large-scale density- and adhesion-controlled ZnO nanorod arrays (NRs) grown on flexible and transparent ITO/PET substrates by simple methods and their mechanism and electrochromic properties are studied as well. Besides, TiO2 nanotube arrays with larger tube clearance are synthesized, and used as a skeleton, two novel hierarchical homogeneous nanoarchitectures of TiO2 nanorods branched TiO2 nanotube arrays (BTs) and P25-coated TiO2 nanotube arrays (PCTs) were synthesized by two-step method. The growth mechanisms of the new nanostructure arrays are explored, among which the focus is on testing and analyzing the properties of TiO2 photovoltaic arrays, UV-Vis absorption spectroscopy and dye-sensitized solar cells, etc. The main content is summarized as follows:1. Using the two-step approach of seed pre-preparation and hydrothermal method, the large-scale density- and adhesion-controlled ZnO NRs could be synthesized on flexible and transparent ITO/PET conductive substrates, which solves the problem that ZnO nanorod arrays could not be directly planted on the flexible transparent substrate. Flexible plastic film could not endure high temperature, but the adoption of low-temperature growth condition enables the synthesis of ZnO nanorods arrays on it. In experiments, various factors were also systematically studied and density-controlled and adhesion-to substrate of ZnO NRs were the focus of the study. Their possible growth mechanism and dynamics were discussed as well. 2. Electrochromic properties of ZnO nanorods arrays were studied by using ZnO nanorods arrays as the working electrode. First, the absorption performances of different density ZnO NRs to electrochromic dye (viologen molecules) were explored. Then, electrochromic properties of different electrode materials were tested, and coloring/bleaching, cyclic voltammetry characteristics curve and other relevant experimental data were analyzed and discussed. As a result, it is found that the color effects, uniformity and transparency of ZnO nanorod arrays with the best dye adsorption electrode are the best and also show the best oxidation-reduction peak.3. By adding the organic solvents such as DMSO into anodizing electrolyte solution, The TiO2 nanotube arrays with larger diameter and tube spacing, longer tube length and rougher surface area (GTs) were successfully synthesized. Compared with TiO2 nanotube arrays (TNAs) synthesized with the traditional anodization, the biggest advantage of the GTs is that it could provide enough space and rough surface for re-modification, thus better for adsorbing various dyes and for getting better photovoltaic performance. Besides, the characterization and the mechanism were studied as well.4. Two innovative technology methods were designed by using ordinary water bath and autoclave equipment. With the GTs of the large tube clearance for the skeleton, two novel nanostructure arrays of hierarchical and homogeneous modification were synthesized:P25-coated TiO2 nanotube arrays (PCTs) and TiO2 nanorods branced TiO2 nanotube arrays (BTs). And various factors affecting the preparation process and possible synthesis mechanism were discussed as well. Furthermore, according to the morphology and phase characterization of BTs and PCTs, it is found that GTs skeleton in BTs and PCTs is anatase, and BTs is the polycrystalline structure composed of the anatase dominated by the GTs and TiO2 nanorods of rutile phase grown on the anatase. And PCTs are the polycrystalline structure composed of GTs and P25 particles.5. Using the four synthesized nanotube arrays based on TiO2 as electrode materials, the performances of their photoelectrochemical, UV-Vis diffuse reflectance spectroscopic spectra and dye-sensitized solar cells were tested and analyzed. The result shows that, compared with TNAs, the photocurrent density and the photoelectric conversion efficiency of GTs with larger tube clearance and longer length, and BTs and PCTs with larger and rougher surface area by modification were greatly improved (that of BTs is relatively higher). And their absorption side band and peak were also greatly improved, that is, the efficiency of light absorption was greatly improved.
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