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Liou Y.-J.,National Dong Hwa University | Chen Y.J.,National Dong Hwa University | Chen Y.J.,Graduate Institute of Optoelectronics Engineering | Chen B.-R.,National Dong Hwa University | And 2 more authors.
Surface and Coatings Technology | Year: 2013

In this study, we demonstrated that the aluminum sec-butoxide solution dip treatment is effective in improving the solar cell efficiency of the dye-sensitized solar cells. By XPS analysis, we successfully illustrate the cause for efficiency improvement. At low dipping concentrations, the efficiency increases, which is due to the formation of the Al2O3 coating on the exposed TiO2 surface that reduces the surface recombination centers. At high dipping concentrations, the efficiency decreases, which is due to the formation of top Al(OH)3 aggregates. The best efficiency achieved at 0.0075M is the result of optimization of the formation of Al2O3 coating while avoiding the formation of top Al(OH)3 aggregates. © 2012 Elsevier B.V.

Chen Y.J.,National Dong Hwa University | Chen Y.J.,Graduate Institute of Optoelectronics Engineering | Lo Y.S.,National Dong Hwa University | Huang C.H.,Graduate Institute of Optoelectronics Engineering | And 2 more authors.
Materials Chemistry and Physics | Year: 2010

A unique method of flat-flame chemical vapor deposition, to synthesize nanostructured TiO2 film used for dye-sensitized solar cells (DSSCs) is reported for the first time. This method produces nanostructures of TiO2 exactly ideal for the anode of the DSSCs. Results show that cells have characteristic I-V curves with fill factor typically around 70% and efficiency higher than 4%. A dendrite-like microstructure of anodes accounts for the high efficiency of the cell. The successful formation of dendrite-like microstructure provides a chance for sintering of TiO2 nanoparticles smaller than 20 nm, a possible cell efficiency enhancement by increased dye absorption due to the increased specific surface area of small particles. © 2009 Elsevier B.V. All rights reserved.

Chen Y.J.,National Dong Hwa University | Chen Y.J.,Graduate Institute of Optoelectronics Engineering | Jhan G.Y.,National Dong Hwa University | Jhan G.Y.,Graduate Institute of Optoelectronics Engineering | And 10 more authors.
Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films | Year: 2010

The authors successfully synthesized titanium oxide (Ti O2) nanopowder with visible-light photocatalytic ability by low-pressure flat-flame metal organic chemical vapor condensation method. In order to confirm that carbon doping is a viable mechanism for the visible-light absorption of the powder prepared by this method, they modify the process by total exclusion of nitrogen usage to eliminate the nitrogen doping possibility. Since nitrogen is avoided in the process, the visible-light absorption cannot be due to nitrogen doping. They also found that the nanopowder formed has a single phase of anatase. Thus the nanopowder does not have anatase/rutile interface, and the authors can eliminate the possibility of visible-light absorption by the anatase/rutile interface. The visible-light absorption should thus be resort to the carbon doping. X-ray photoelectron spectroscopy studies show the presence of several carbon related bonds except Ti-C bond. This suggests that the carbon does not incorporate into the Ti O2 crystal and should locate on the surface of the nanopowder. Thus the carbon species act as a visible-light sensitizer for the Ti O2 as a photocatalyst. Among all carbon bonds the C-C bond is believed to be responsible for the light absorption, since all other carbon related bonds are not chromophores. The visible-light Ti O 2 photocatalysis induced by carbon doping is confirmed and explained. © 2010 American Vacuum Society.

Chen Y.J.,National Taiwan University | Chen Y.J.,Graduate Institute of Optoelectronics Engineering | Shih Y.Y.,National Taiwan University | Shih Y.Y.,Graduate Institute of Optoelectronics Engineering | And 6 more authors.
Ceramics International | Year: 2010

ZnO growth on sapphire by MOCVD using dimethylzinc and CO2 as zinc and oxygen precursors was performed. A dense ZnO film with major (0 0 0 2) orientation can be prepared at 350 °C and above with high dimethylzinc flow rate. Result shows that the growth temperature suppresses the lateral growth of ZnO grains, promotes the coalescence of grains but reduces the crystal alignment. To further enhance the crystal alignment, a two-step temperature variation growth method is proposed. Using the two-step growth method, employing the initial growth at lower temperature followed by the growth at higher temperature, a densely packed ZnO film with larger grains and well-aligned (0 0 0 2) crystallographic orientation can be obtained. The effect of temperature on nucleation and growth rate, and its relation to the crystal alignment enhancement is also discussed. © 2009 Elsevier Ltd and Techna Group S.r.l.

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