Browsing by Author "Wu, Jenn-Ming"

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Efficient electron transport in tetrapod-like ZnO metal-free dye-sensitized solar cells
(2009)
Chiu, Wei-Hao
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Lee, Chia-Hua
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Cheng, Hsin-Ming
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Lin, Hsiu-Fen
;
Liao, Shih-Chieh
The tetrapod-like ZnO nanopowders are employed to construct an efficient electron transport network as the photoanode of the dye-sensitized solar cells (DSCs). Due to the high extinction coefficient of the metal-free D149 dye offering a high photocurrent through the ZnO network, the best performance of DSCs based on a 42 mu m terapod-like ZnO film showed a high energy conversion efficiency of 4.9% with a high short-circuit photocurrent density of 12.3 mA cm(-2), an open-circuit photovoltage of 0.6 V, and a fill factor of 0.65 under AM 1.5 irradiation. Highly efficient electron transport may also be ascribed by a long effective electron diffusion length of 46 mu m determined from the electrochemical impedance spectroscopy which is consistent with thickness dependent J(SC) measurements.
Improved performance of flexible dye-sensitized solar cells by introducing an interfacial layer on Ti substrates
(2011)
Lee, Chia-Hua
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Chiu, Wei-Hao
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Lee, Kun-Mu
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Hsieh, Wen-Feng
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Wu, Jenn-Ming
The recombination reaction of injected electrons with triiodide ion in the electrolyte limits the efficiency of dye-sensitized solar cells (DSSCs). This study reports the preparation of a sponge-like and conformal TiO(2) underlayer by hydrogen peroxide oxidation of Ti foil. This underlayer serves as a charge recombination barrier layer at the nanocrystalline TiO(2)/substrate interface, and suppresses the recombination reaction. This sponge-like TiO(2) underlayer increases the electrical contact area between the Ti substrate and nanocrystalline TiO(2), helping nanocrystalline TiO(2) attach to the Ti substrate. This study compares the performance of DSSCs that were subjected to different Ti surface treatments. Electrochemical impedance spectroscopy results confirm that the proposed sponge-like TiO(2) underlayer increased the open-current voltage (V(OC)) and fill factor (FF) due to prolonged electron life time (tau(eff)), and minimized resistance at the TiO(2)/Ti interface (R(CT)). With an optimal thickness of nanocrystalline TiO(2) and concentration of I(2), we achieved a conversion efficiency of 6.75% for a back-illuminated DSSC.
Phase-driven magneto-electrical characteristics of single-layer MoS2
(2016)
Yang, Chao-Yao
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Chiu, Kuan-Chang
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Chang, Shu-Jui
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Zhang, Xin-Quan
;
Liang, Jaw-Yeu
Magnetism of the MoS2 semiconducting atomic layer was highlighted for its great potential in the applications of spintronics and valleytronics. In this study, we demonstrate an evolution of magneto-electrical properties of single layer MoS2 with the modulation of defect configurations and formation of a partial 1T phase. With Ar treatment, sulfur was depleted within the MoS2 flake leading to a 2H (low-spin) -> partial 1T (high-spin) phase transition. The phase transition was accompanied by the development of a ferro-magnetic phase. Alternatively, the phase transition could be driven by the desorption of S atoms at the edge of MoS2 via O-2 treatment while with a different ordering magnitude in magnetism. The edge-sensitive magnetism of the single-layer MoS2 was monitored by magnetic force microscopy and validated by a first-principle calculation with graded-Vs (sulfur vacancy) terminals set at the edge, where band-splitting appeared more prominent with increasing Vs. Treatment with Ar and O-2 enabled a dual electrical characteristic of the field effect transistor (FET) that featured linear and saturated responses of different magnitudes in the I-ds-V-ds curves, whereas the pristine MoS2 FET displayed only a linear electrical dependency. The correlation and tuning of the Vs-1T phase transition would provide a playground for tailoring the phase-driven properties of MoS2 semiconducting atomic layers in spintronic applications.
Synthesis and Characterization of One-Dimensional Ag-Doped ZnO/Ga-Doped ZnO Coaxial Nanostructure Diodes
(2014-04-09)
Chiu, Hsien-Ming
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Chang, Yu-Tsui
;
Wu, Wen-Wei
;
Wu, Jenn-Ming
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材料科學與工程學系
In the pursuit of high injection current diode nanodevices, entire one-dimensional (1D) ZnO coaxial nanostructures with p-n homojunctions is one of the ideal structures. In this study, we synthesized entire 1D ZnO-based coaxial homojunction diodes with p-type Ag-doped ZnO (SZO) nanostructure shells covering n-type Ga-doped ZnO (GZO) nanopagoda (NPG) cores by a metal organic chemical vapor deposition (MOCVD) technique. The entire ID SZO-GZO and SZO-ZnO coaxial nanostructures exhibit better diode characteristics, such as lower threshold voltage, better rectification ratios, and better ideality factor n, than that reported for either 2D or 2D-1D p-n heterojunction and/or homojunction diodes. The binding energies of Ga and Ag were evaluated by low-temperature and temperature-dependent photoluminescence. In comparison, the SZO-GZO coaxial p-n nanostructures display better diode performance than the SZO-ZnO ones.
The influence of tetrapod-like ZnO morphology and electrolytes on energy conversion efficiency of dye-sensitized solar cells
(2010-12-01)
Lee, Chia-Hua
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Chiu, Wei-Hao
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Lee, Kun-Mu
;
Yen, Wen-Hsiang
;
Lin, Hsiu-Fen
Tetrapod-like ZnO nanostructures prepared by dc plasma technology were used as photoelectrodes in dye-sensitized solar cells (DSSCs) Each of the tetrapod-like ZnO possesses four extended arms that offer improved electron transport properties Tetrapod-like ZnO with short (S-ZnO) and long arms (L-ZnO) were synthesized by controlling the plasma gas flow and the input power Between these two tetrapod-like ZnO nanopowders the DSSCs using S-ZnO showed higher energy conversion efficiency than using L-ZnO This is due to the resulting increase in dye adsorption and enhanced short-circuit current density using S-ZnO Electrochemical Impedance spectroscopy (EIS) shows that the properties of electron transport of S-ZnO are superior to that of the L-ZnO We investigated the effect of the redox electrolytes (12) and the additives (Lil and TBP) on the performance of the DSSCs by intensity-modulated photovoltage spectroscopy and EIS (C) 2010 Elsevier Ltd All rights reserved