Browsing by Author "Wang, Niann S."

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Detachment and transfer of ordered TiO(2) nanotube arrays for front-illuminated dye-sensitized solar cells
(2011-09-01)
Li, Lu-Lin
;
Chen, Yi-Ju
;
Wu, Hui-Ping
;
Wang, Niann S.
;
Diau, Eric Wei-Guang
We report a method of detachment and transfer of one-dimensional TiO(2) nanotube (NT) arrays to fabricate dye-sensitized solar cells (DSSCs) with illumination from the front side. The ordered NT arrays (tube length 20 mm) were detached from the NT-Ti substrate, as annealed, by means of a second anodization at 20 V for 4 h and then transferred, inverted, onto a transparent substrate of conducting oxide (TCO) with an interface of TiO(2) nanoparticles of thickness similar to 2 mu m. Dry etching of the NT surface in a highly dense plasma reactor under BCl(3)/Cl(2) for 90 s opened previously closed ends of the tubes. The inverted (bottom-up) NT-TCO substrate was fabricated into a DSSC device that shows a cell performance (eta = 6.24%) significantly improved over those of a front-illuminated counterpart with an upright (face-up) structure (eta = 4.84%) and of a conventional back-illuminated device (eta = 4.61%). Electrochemical impedance spectra (EIS) of the devices under one-sun irradiation were measured to rationalize the cell performances that are consistent with the corresponding interfacial impedances between the NT arrays and the electrode for collection of electrons.
Detachment and transfer of ordered TiO2 nanotube arrays for front-illuminated dye-sensitized solar cells
(2011-09-01)
Li, Lu-Lin
;
Chen, Yi-Ju
;
Wu, Hui-Ping
;
Wang, Niann S.
;
Diau, Eric Wei-Guang
We report a method of detachment and transfer of one-dimensional TiO2 nanotube (NT) arrays to fabricate dye-sensitized solar cells (DSSCs) with illumination from the front side. The ordered NT arrays (tube length 20 mm) were detached from the NT-Ti substrate, as annealed, by means of a second anodization at 20 V for 4 h and then transferred, inverted, onto a transparent substrate of conducting oxide (TCO) with an interface of TiO2 nanoparticles of thickness similar to 2 mu m. Dry etching of the NT surface in a highly dense plasma reactor under BCl3/Cl-2 for 90 s opened previously closed ends of the tubes. The inverted (bottom-up) NT-TCO substrate was fabricated into a DSSC device that shows a cell performance (eta = 6.24%) significantly improved over those of a front-illuminated counterpart with an upright (face-up) structure (eta = 4.84%) and of a conventional back-illuminated device (eta = 4.61%). Electrochemical impedance spectra (EIS) of the devices under one-sun irradiation were measured to rationalize the cell performances that are consistent with the corresponding interfacial impedances between the NT arrays and the electrode for collection of electrons.
Kinetics and Mechanism of the NCN+NO2 Reaction Studied by Experiment and Theory
(2008-10-16)
Yang, Tsung-Ju
;
Wang, Niann S.
;
Lee, L. C.
;
Xu, Z. F.
;
Lin, M. C.
The rate constant for the NCN + NO2 reaction has been measured by a laser photolysis/laser-induced fluorescence technique in the temperature range of 260-296 K at pressures between 100 and 500 Torr with He and N-2 as buffer gases. The NCN radical was produced from the photolysis of NCN3 at 193 nm and monitored by laser-induced fluorescence with a dye laser at 329.01 nm. The rate constant was found to increase with pressure but decrease with temperature, indicating that the reaction occurs via a long-lived intermediate stabilized by collisions with buffer gas. The reaction mechanism and rate constant are also theoretically predicted for the temperature range of 200-2000 K and the He and N-2 pressure range of 10(-4) Torr to 1000 atm based on dual-channel Rice-Ramsperger-Kassel-Marcus (RRKM) theory with the potential energy surface evaluated at the G2M//B3LYP/6-311+G(d) level. In the low-temperature range (< 700 K), the most favorable reaction is the barrierless association channel that leads to the intermediate complex (NCN-NO2). At high temperature, the direct O-abstraction reaction with a barrier of 9.8 kcal/mol becomes the dominant channel. The rate constant calculated by RRKM theory agrees reasonably well with experimental data.