• Korean Journal of Materials Research
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• v.21 no.2
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• pp.111-114
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• 2011

As a growth-template of ZnO nanorods (NR), a hexagonal $\beta-Ni(OH)_2$ nanosheet (NS) was synthesized with the low temperature hydrothermal process and its microstructure was investigated using a high resolution scanning electron microscope and transmission electron microscope. Zinc nitrate hexahydrate was hydrolyzed by hexamethylenetetramine with the same mole ratio and various temperatures, growth times and total concentrations. The optimum hydrothermal processing condition for the best crystallinity of hexagonal $\beta-Ni(OH)_2$ NS was determined to be with 3.5 mM at $95^{\circ}C$ for 2 h. The prepared $Ni(OH)_2$ NSs were two dimensionally arrayed on a substrate using an air-water interface tapping method, and the quality of the array was evaluated using an X-ray diffractometer. Because of the similarity of the lattice parameter of the (0001) plane between ZnO (wurzite a = 0.325 nm, c = 0.521 nm) and hexagonal $\beta-Ni(OH)_2$ (brucite a = 0.313 nm, c = 0.461 nm) on the synthesized hexagonal $\beta-Ni(OH)_2$ NS, ZnO NRs were successfully grown without seeds. At 35 mM of divalent Zn ion, the entire hexagonal $\beta-Ni(OH)_2$ NSs were covered with ZnO NRs, and this result implies the possibility that ZnO NR can be grown epitaxially on hexagonal $\beta-Ni(OH)_2$ NS by a soluble process. After the thermal annealing process, $\beta-Ni(OH)_2$ changed into NiO, which has the property of a p-type semiconductor, and then ZnO and NiO formed a p-n junction for a large area light emitting diode.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.71-71
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• 2011

Dye-sensitized solar cells (DSCs) have drawn great academic attention due to their potential as low-cost renewable energy sources. DSCs contain a nanostructured TiO2 photoanode, which is a key-component for high conversion efficiency. Particularly, one-dimensional (1-D) nanostructured photoanodes can enhance the electron transport for the efficient collection to the conducting substrate in competition with the recombination processes. This is because photoelectron colletion is determined by trapping/detrapping events along the site of the electron traps (defects, surface states, grain boundaries, and self-trapping). Therefore, 1-D nanostructured photoanodes are advantageous for the fast electron transport due to their desirable features of greatly reduced intercrystalline contacts with specified directionality. In particular, anodic TiO2 nanotube (NT) electrodes recently have been intensively explored owing to their ideal structure for application in DSCs. Besides the enhanced electron transport properties resulted from the 1-D structure, highly ordered and vertically oriented nanostructure of anodic TiO2 NT can contribute additional merits, such as enhanced electrolyte diffusion, better interfacial contact with viscous electrolytes. First, to confirm the advantages of 1-D nanostructured material for the photoelectron collection, we compared the electron transport and charge recombination characteristics between nanoparticle (NP)- and nanorod (NR)-based photoanodes in DSCs by the stepped light-induced transient measurements of photocurrent and voltage (SLIM-PCV). We confirmed that the electron lifetime of the NR-based photoanode was much longer than that of the NP-based photoanode. In addition, highly ordered and vertically oriented TiO2 NT photoanodes were prepared by electrochemical anodization method. We compared the photovoltaic properties of DSCs utilizing TiO2 NT photoanodes prepared by one-step anodization and two-step anodization. And, to reduce the charge recombination rate, energy barrier layer (ZnO, Al2O3)-coated TiO2 NTs also applied in DSC. Furthermore, we applied the TiO2 NT photoanode in DSCs using a viscous electrolyte, i.e., cobalt bipyridyl redox electrolyte, and confirmed that the pore structure of NT array can enhance the performances of this viscous electrolyte.