Hong-Wen Wang

Three-dimensional electrodes for dye-sensitized solar cells: synthesis of indium?tin-oxide nanowire arrays and ITO/TiO2 core?shell nanowire arrays by electrophoretic deposition

Dye-sensitized solar cells (DSSCs) show promise as a cheaper alternative to silicon-based photovoltaics for specialized applications, provided conversion efficiency can be maximized and production costs minimized. This study demonstrates that arrays of nanowires can be formed by wet-chemical methods for use as three-dimensional (3D) electrodes in DSSCs, thereby improving photoelectric conversion efficiency. Two approaches were employed to create the arrays of ITO (indium-tin-oxide) nanowires or arrays of ITO/TiO(2) core-shell nanowires; both methods were based on electrophoretic deposition (EPD) within a polycarbonate template. The 3D electrodes for solar cells were constructed by using a doctor-blade for coating TiO(2) layers onto the ITO or ITO/TiO(2) nanowire arrays. A photoelectric conversion efficiency as high as 4.3% was achieved in the DSSCs made from ITO nanowires; this performance was better than that of ITO/TiO(2) core-shell nanowires or pristine TiO(2) films. Cyclic voltammetry confirmed that the reaction current was significantly enhanced when a 3D ITO-nanowire electrode was used. Better separation of charge carriers and improved charge transport, due to the enlarged interfacial area, are thought to be the major advantages of using 3D nanowire electrodes for the optimization of DSSCs.

Standing [111] gold nanotube to nanorod arrays via template growth

Standing [111]-oriented crystalline gold nanotube (AuNT) and nanorod (AuNR) arrays using electrochemical deposition through template growth are reported. Segments of single crystal and bamboo-like crystalline AuNR arrays with growing direction of [111], having a diameter of 100-150xa0nm and a length of 10xa0µm, standing perpendicular to Ti metal foil substrates, are synthesized. The as-synthesized AuNTs and AuNRs are characterized by powder and five circle x-ray diffractometry, UV-visible molecular absorption spectrometry, field emission scanning electron microscopy, and transmission electron microscopy. AuNRs and AuNTs are formed by starting with a tube and the wall of the tube gets progressively thicker and eventually sealed up to form nanorods. Optical absorption at 548 and 578xa0nm wavelength for gold nanotubes and nanorods, respectively, caused by the transverse (width) mode is identified.

A generalized optimal path-selection model for structural program testing

Abstract Economic and effective preparation of test cases involves identification of the minimal set of test paths that meets certain test requirements. Unlike traditional approaches that employ heuristic algorithms, we solve this problem on the basis of a rigid mathematical ground. This article discusses how the path-selection problem in structural program testing can be formulated as a zero-one integer programming problem. It is thus possible to find the solution through one of the most powerful problem-solving techniques in the realm of operations research. The model applies not only to common requirements such as statement and branch testing. This generalized model has greater merits. A large variety of constraints, cost functions, and coverage requirements can easily be handled as special cases of the same integer programming problem.

Dye-sensitized solar cells based on indium-tin oxide nanowires coated with titania layers

The concept of growing ITO (Indium-Tin-oxide) or ITO/TiO2 core-shell nanowire arrays for the use of 3D electrodes in dye-sensitized solar cells (DSSCs) has been tested in the present study. By employing the template electrophoretic deposition (EPD) method, ITO and ITO/TiO2 nanowire arrays were synthesized. A 3D electrode for DSSCs was constructed using a doctor blade to coat TiO2 layers covering the ITO or ITO/TiO2 nanowire arrays. The separation of charge generation, charge transport functions, enlarged interface area were thought to be the major advantages of 3D nanowire electrodes for the optimization of DSSCs. Photoelectric conversion efficiency at 3.99% of the DSSCs made from ITO nanowires was obtained, which was much higher than those of ITO/TiO2 core- shell nanowire arrays or pristine TiO2 films. The morphology of ITO/TiO2 core-shell nanowire arrays is sensitive to fabrication process and significantly affects the final performance. Cyclic voltammetry confirmed that the reaction current was significantly enhanced when a 3D ITO nanowire electrode was used.

A Facile Way to Form a Graded Halide Layer in Perovskite Solar Cells

A light harvest layer composed of gradual change from formamidinium lead triiodide (FAPbI₃) to methylammonium lead triiodide (MAPbI₃) was fabricated using a novel two-step process. That is, a graded halide layer structure without extra processing steps is demonstrated. Conventionally, in the fabrication of MAPbI₃ perovskite solar cells (PSCs) using two-step process, PbI₂ layer was the first deposited on a mesoporous TiO₂ coated substrate. The methylammonium iodide (MAI) solvent was then spin-coated on the surface of PbI₂ layer and heated to form the MAPbI₃ perovskite layer. Double perovskite layers such as FAPbI₃ plus MAPbI₃ requires twice of the second step which FAI and MAI should be spin-coated individually. This can be tedious and time consuming. We report here a facile way to form a graded perovskite layer, consisting FAPbI₃ to MAPbI₃, in a single step. FAI was first added into dimethylformamide (DMF) solution that was used to form PbI₂ layer, then MAI solution was dripped on top of the FAI/PbI₂ layer. The graded perovskite layer structure (FAPbI₃/MAPbI₃) in a gradient manner are readily formed, where the structure is confirmed by EDS to be FTO/compact TiO₂/mesoporous TiO₂/FAPbI₃(thin)/MAPbI₃/Spiro-OMeTAD/Ag. The Jsc, and Voc of solar cells with this graded perovskite layer are enhanced and the efficiency increases from 11.62% to 14.06%.

Rapid Hydrogen Generation from the Reaction of Aluminum Powders and Water Using Synthesized Aluminum Hydroxide Catalysts

A synthesized and nano-sized Al(OH)3 powder that promotes the generation of hydrogen from a Al/water reaction is demonstrated. In this study, aluminum hydroxides are synthesized using sodium aluminate NaAlO2, distilled water and ethanol. The mole ratio of ethanol/water and the concentration of sodium aluminate in solution affect the crystal structure, morphology and sizes of the Al(OH)3 powders significantly. These Al(OH)3 powders contain both gibbsite and bayerite phases and exhibit excellent catalytic power on the hydrogen generation of Al/water system. It is proposed that two major characteristics of Al(OH)3 powders dominate the catalytic power. That is, the surface area and the high-energy sites of Al(OH)3. When mole ratio of ethanol/water is between 0.3–0.6 and the concentration of NaAlO2 is higher than 0.0167xa0g/ml, the synthesized Al(OH)3 powders are in a more gibbsite-oriented and plate-like structure. Other than above conditions result in a more bayerite-oriented and particulate-like structure. The plate-like structure exhibits strong catalytic power due to the existence of high-energy sites on the edge of plates even its surface area is not so high. The particulate-like structure may also have strong catalytic power when it has a high surface area. By taking advantage of the exothermic reaction, ~u2009100% yield of hydrogen can be produced from 1xa0g Al/10xa0g water system within 30xa0s using 3xa0g synthesized Al(OH)3. A aluminum waste scrap can also react with water using these effective catalysts and generateu2009~u200995% yield of hydrogen within 8xa0min.

Synthesis and characterization of highly ordered TiO 2 nanotube arrays

Highly-ordered TiO2 nanotube arrays (TNA) by anodizing Ti foil were carried out using a slightly modified electrochemical process. The parameters such as anodization potentials and duration have been varied in order to fabricate the specific length and diameter of TNA. The morphologies of TNA were characterized by field emission scanning electron microscope (Hitachi S-4100 FE-SEM). The crystalline phase and structure were analyzed using X-ray diffraction (Rigaku, XRD). The processing anodic current density with time was recorded by Keithley 2400. The photocurrents induced by UV-light were characterized by CHI 611. The performance of hydrogen production from photoelectrocatalytic effect of larger diameter TNA is found to be higher than the smaller diameter TNA. Base on the microstructure and calculation, we confirmed that larger diameter TNA do exhibit higher surface area.