Dielectrophoretic assembly of ZnO nanowires

The synthesis of zinc oxide （ZnO） nanowires is achieved by vapor phase transportation （VPT） method. The designed quartz tube, whose both ends are narrow and the middle is wider, is used to control the growth of ZnO nanowires. Dielectrophoresis （DEP） method is employed to align and manipulate ZnO nanowires which are ultrasonic dispersed and suspended in ethanol solution. Under the dielectrophoretic force, the nanowires are trapped on the pre-patterned electrodes, and further aligned along the electric field and bridge the electrode gap. The dependence of the alignment yield on the applied voltage and frequency is investigated.     

Patterned growth of ZnO nanofibers

A simple method is adopted to grow ZnO nanofibers laterally among the patterned seeds designed in advance on silicon substrate. The preparation of seed lattices is carried out by lithographing the metal zinc film evaporated on the substrate. A layer of aluminum is covered on the zinc layer to prevent the ZnO nanorods vertically growing on the top surface. After oxidation, the patterned ZnO/Al2O3 spots are formed at the sites for the horizontal growth of ZnO nanofibers by the vapor phase transportation （VPT） method using the zinc powders as source material.     

Performances of ZnO-Based Dye Sensitized Solar Cells Fabricated by Hydrothermal Synthesis and Sol-Gel Technique

ZnO is introduced as an alternative to TiO2 in dye sensitized solar cells （DSSCs） due to its band gap similar to TiO2, higher electron mobility, and flexible procedures of preparations. Several samples of ZnO films are prepared with the hydrothermal synthesis method and the sol-gel technique, respectively. These ZnO films were assembled as photoanodes in DSSCs using N3 dye as the sensitizer. The ZnO-based cells prepared by the hydrothermal synthesis show typical current source characteristics, whose fill factor （FF） is 0.44 and photo-to-electric power conversion efficiency is 0.34%. On the other hand, all the samples prepared with the sol-gel technique show accompanied source characteristics with relatively higher power conversion efficiencies （1%） but a lower FF （0.26）. X-ray diffraction （XRD） and atomic force microscopy （AFM） measurements indicate that the sol-gel samples have small particles sizes. Therefore, sol-gel samples could adsorb more dye molecules to generate high conversion efficiencies. At the same time, more grain boundaries make it more possible for injected electrons to recombine with the oxidized electrolyte. Hydrothermal samples have bigger grains, so they show poor conversion efficiency and relatively high FF.