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Qiu, Jijun,Li, Xiaomin,Zhuge, Fuwei,Gan, Xiaoyan,Gao, Xiangdong,He, Weizhen,Park, Se-Jeong,Kim, Hyung-Kook,Hwang, Yoon-Hwae IOP Pub 2010 Nanotechnology Vol.21 No.19
<P>Well-aligned ZnO nanowire arrays with a long length of more than 40 mu m were prepared successfully by using the polyethylenimine (PEI)-assisted preheating hydrothermal method (PAPHT). Several important synthetic parameters such as PEI content, growth time, preheating time and zinc salt concentration were found to determine the growth of ultralong ZnO nanowire arrays, including length, diameter, density and alignment degree. The photoluminescence (PL) spectrum of as-grown ultralong ZnO nanowire arrays revealed a UV emission and a yellow emission, which was attributed to the absorbed hydroxyl group based on the peak shift after annealing in various atmospheres. The performance of dye-sensitized solar cells (DSSCs) increased with increasing length of ZnO nanowire arrays, which was mainly ascribed to the aggrandized photocurrent and reduced recombination loss according to electrochemical impedance spectroscopy (EIS). A maximum efficiency of 1.3% for a cell with a short-circuit current density (J(sc)) = 4.26 mA cm(2), open-circuit voltage (V-oc) = 0.69 V and (fill factor) FF = 0.42 was achieved with a length of 40 mu m.</P>
Qiu, Jijun,Li, Xiaomin,He, Weizhen,Park, Se-Jeong,Kim, Hyung-Kook,Hwang, Yoon-Hwae,Lee, Jae-Ho,Kim, Yang-Do IOP Pub 2009 Nanotechnology Vol.20 No.15
<P>Well-aligned ultralong ZnO nanorod arrays with a length of 10 µm have been synthesized on glass substrates using a preheating hydrothermal method. The diameter of the nanorods is in the range from 50 to 80 nm, and the aspect ratio and alignment can be simply controlled by varying the preheating time. Based on the evolution of aspect ratio with preheating time, a possible growth mechanism was proposed. X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that the nanostructures are well oriented with the <I>c</I>-axis perpendicular to the substrate. The photoluminescence (PL) spectrum of the as-grown ZnO nanostructure reveals a near-band-edge (NBE) emission peak and a yellow emission, and the origin of yellow emission was confirmed to be from the absorbed hydroxyl group. The ultralong nanorod arrays made in solution have a desirable diameter, length, density and orientation for ordered nanodevice applications. </P>
Jijun Qiu,Dong-Myeong Shin,Weizhen He,김형국,황윤회,Xiaomin Li,Xiangdong Gao 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.9
Axially (c-axis)-oriented ZnO thick films with a 8.1 μm thickness were fabricated on ZnOseed layer coated substrates by using a filtered preheated hydrothermal solution. The thick filmscomposed of single-crystal ZnO microrods with various diameters were formed by coalescing eachnanorod together along their side surfaces. From the X-ray diffraction result a biaxial stress existswas found to exist in the as-grown thick films, and the stress gradually increased with increasingannealing temperatures from 200 to 550 C due to a degradation in the crystalline quality. Thebiaxial stress is responsible for the red-shift of the optical band gap of the ZnO thick films. Photoluminescenceand Hall results revealed that the optical and the electrical properties of the thick filmswere degenerated after high-temperature annealing (> 200 C), which was due to the introductionof point defects, such as oxygen interstitials and zinc vacancies.
Qiu, Jijun,Weng, Binbin,Zhao, Lihua,Chang, Caleb,Shi, Zhisheng,Li, Xiaomin,Kim, Hyung-Kook,Hwang, Yoon-Hwae Hindawi Limited 2014 Journal of nanomaterials Vol.2014 No.-
<P>Flower-like bundles of ZnO nanosheets have been prepared by using preheating hydrothermal process without any surfactants. The flower-like bundles consist of many thin and uniform hexagonal-structured ZnO nanosheets, with a thickness of 50 nm. The selected area electronic diffraction (SAED) and high-resolution transmission electron microscope (HRTEM) images indicate that the ZnO nanosheets are single crystal in nature. The growth mechanism of the flower-like bundles of ZnO nanosheets is discussed based on the morphology evolution with growth times and reaction conditions. It is believed that the formation of flower-like bundles of ZnO nanosheets is related to the shielding effect of OH<SUP>−</SUP>ions and the self-assembly process, which is dominated by a preheating time. Room temperature photoluminescence spectra results show that the annealing atmosphere strongly affects the visible emission band, which is sensitive to intrinsic and surface defects, especially oxygen interstitials, in flower-like bundles of ZnO nanosheets.</P>
The fabrication of TiO2 mesoporous thick films by employing a pre-embedded ZnO nanorods support.
He, Weizhen,Qiu, Jijun,Park, Se-Jeong,Lee, Jea-Ho,Kim, Yang-Do,Kim, Hyung-Kook,Hwang, Yoon-Hwae American Scientific Publishers 2009 Journal of Nanoscience and Nanotechnology Vol.9 No.12
<P>TiO2 mesoporous films with a thickness more than 2 microm were synthesized through the evaporation-induced self-assembly approach. In order to prevent the formation of cracks due to the strain during the calcination, we employed the ZnO nanorod arrays as a pre-embedded support, which were obtained from an aqueous solution method. The spaces between ZnO nanorods were filled with TiO2 sol-gel by a dip-coater. Then ZnO nanorods embedded in the thick film were eliminated by a wet chemical etching method and the left spaces were refilled by the TiO2 sol-gel. As a result, a dense and thick TiO2 mesoporous film was obtained. The resultant materials were characterized in detail by using small angle X-ray diffraction (SAXRD), field-emission scanning electron microscopy (FESEM) and transmission electron microscopy methods (TEM).</P>
Advantages of using Ti-mesh type electrodes for flexible dye-sensitized solar cells
He, Weizhen,Qiu, Jijun,Zhuge, Fuwei,Li, Xiaomin,Lee, Jae-Ho,Kim, Yang-Do,Kim, Hyung-Kook,Hwang, Yoon-Hwae IOP Pub 2012 Nanotechnology Vol.23 No.22
<P>We used Ti meshes for both the photoanodes and counter electrodes of dye-sensitized solar cells (DSSCs) to improve the flexibility and conductivity of the electrodes. These mesh type electrodes showed good transparency and high bendability when subjected to an external force. We demonstrated the advantages of cells using such electrodes compared to traditional transparent conducting oxide based electrodes and back side illuminated DSSCs, such as low sheet resistance, elevated photo-induced current and enhanced sunlight utilization. Nanotube layers of different thicknesses were investigated to determine their effect on the photovoltaic parameters of the cell. The overall efficiency of the best cells was approximately 5.3% under standard air mass 1.5 global (AM 1.5 G) solar conditions. Furthermore, the DSSCs showed an efficiency of approximately 3.15% due to the all Ti-mesh type electrodes even after illumination from the back side.</P>
Fabrication of Volmer-Weber type ZnO nanorods by combining RF sputtering and hydrothermal methods.
Park, Se-Jeong,Qiu, Jijun,He, Weizhen,Namgung, Wan,Kim, Yang-Do,Lee, Jae-Ho,Hwang, Yoon-Hwae,Kim, Hyung-Kook American Scientific Publishers 2009 Journal of Nanoscience and Nanotechnology Vol.9 No.12
<P>We fabricated Volmer-Weber type ZnO nanorods by using a hydrothermal method combing with an RF sputtering system. Volmer-Weber type ZnO seed nanocrystals were formed on Pt(111)/TiO2/SiO2/Si(100) substrates by using RF sputtering method and then the seeded substrates were soaked in an aqueous chemical solution, which was mixed with Zn(NO3)2 x 6H2O and NaOH. We found that ZnO nanorods were perpendicularly grown along the [002] direction by using X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. We also confirmed that fabricated ZnO nanorods were Volmer-Weber type by using an energy dispersive X-ray spectrometer (EDX) method.</P>