Browsing by Author "Lin, Tai-Yuan"

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Achieving graded refractive index by use of ZnO nanorods/TiO2 layer to enhance omnidirectional photovoltaic performances of InGaP/GaAs/Ge triple-junction solar cells
(2015-05-01)
Tsai, Meng-Tsan
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Yang, Zu-Po
;
Jing, Ting-Shivan
;
Hsieh, Hsing-Hua
;
Yao, Yung-Chi
In this study, we theoretically and experimentally demonstrate high performance of antireflection (AR) coating composed of the ZnO nanorods (NRs) and TiO2 layers applied on InGaP/GaAs/Ge triple-junction solar cells. The high performance of this AR coating is due to the realization of a smooth gradient profile of refractive index fabricated by only two physical layers. First, due to the inherent inhomogeneous-nanoporous geometry along the surface normal, the ZnO NRs are reasonable to be considered as discrete multiple optical layers with low scattering loss, leading to the index smoothly increasing from air ambient toward down to the solar cells. Second, to compensate the gap of index between ZnO and solar cells, an additional TiO2 layer with index in between is hence necessary to insert under ZnO NRs, significantly further reducing the Fresnel reflection loss of the entire device. The ZnO NRs/TiO2 layer shows a low wavelength-averaged (solar spectrum weighted) reflectance of 6.00% (4.78%) over a wide spectral range of lambda=380-1800 nm, and exhibits a hydrophobic surface with a water contact angle of 128.2 degrees. At device level, we compared the photovoltaic performance of solar cells with and without AR coating, the short-circuit density (J(SC)) is enhanced by 31.8% and 23.8% for solar cells integrated with the ZnO NR5/TiO2 layer and conventional SiO2/TiO2 double-layer AR (DLAR) coating, respectively. Under a very large incident angle of solar illumination (theta=80 degrees), the ZnO NRs/TiO2 layer remains static with J(SC) enhancement of 35.2%, whereas the J(SC) enhancement of conventional DLAR coating drops down to 9.4%. In addition, the ZnO NRs/TiO2 layer barely affects the open-circuit voltage and fill factor of the solar device. Therefore, the proposed ZnO NR5/TiO2 layer with a smoother graded refractive index change is highly promising for the AR coating applications for the next-generation solar cells. (C) 2014 Elsevier B.V. All rights reserved.
Annealing effects on the p-type ZnO films fabricated on GaAs substrate by atmospheric pressure metal organic chemical vapor deposition
(2011-02-03)
Huang, Yen-Chin
;
Weng, Li-Wei
;
Uen, Wu-Yih
;
Lan, Shan-Ming
;
Li, Zhen-Yu
The effects of post-annealing conducted at 500-650 degrees C on structural, electrical and optical properties of ZnO film fabricated on GaAs (1 0 0) substrate by atmospheric pressure metal-organic chemical vapor deposition are investigated. X-ray diffraction analyses show that the Zn(3)As(2) and ZnGa(2)O(4) phases are produced for the specimens post-annealed at 500 degrees C and above. Hall measurements indicate that stable p-type ZnO films with hole concentration ranging from 4.7 x 10(18) to 8.7 x 10(19) cm(-3) can be obtained by modulating the annealing temperature from 500 to 600 degrees C. In particular, room-temperature photoluminescence (PL) measurements indicate that the superior-quality p-type film could be achieved by a post-annealing treatment at 600 degrees C. Moreover, low temperature PL spectra at 10 K are dominated by the acceptor-related luminescence mechanisms for the films post-annealed at 550 degrees C and above. The ionization energy of acceptor was calculated to be 133-146 meV, which is in good agreement with that theoretically predicted for the As(Zn)-2V(Zn), complex in ZnO. The interdiffused arsenic atoms in the film post-annealed at 600 inverted perpendicular C are suggested to form the As(Zn)-2V(Zn) complex quite effectively, resulting in the most enhanced p-type conductivity and improved material quality. (C) 2010 Elsevier B.V. All rights reserved.
Characterizations of Ga-doped ZnO films on Si (111) prepared by atmospheric pressure metal-organic chemical vapor deposition
(2009-11-01)
Huang, Yen-Chin
;
Li, Zhen-Yu
;
Weng, Li-Wei
;
Uen, Wu-Yih
;
Lan, Shan-Ming
Gallium-doped ZnO films were grown on p-Si(111) substrates by atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD) using diethylzinc and water as reactant gases and triethyl gallium (TEG) as a n-type dopant gas. The structural, electrical, and optical properties of ZnO:Ga films obtained by varying the flow rate of TEG from 0.56 to 3.35 mu mol/min were examined. X-ray diffraction patterns and scanning electron microscopy images indicated that Ga doping plays a role in forming microstructures in ZnO films. A flat surface with a predominant orientation (101) was obtained for the ZnO:Ga film fabricated at a flow rate of TEG = 2.79 mu mol/min. This film also revealed a lowest resistivity of 4.54 x 10(-4) Omega cm, as measured using the van der Pauw method. Moreover, low temperature photoluminescence (PL) emission recorded at 12 K demonstrated the Burstein Moss shift of PL line from 3.365 to 3.403 eV and a line broadening from 100 to 165 meV as the TEG flow rate varied from 0.56 to 2.79 mu mol/min. This blueshift behavior of PL spectra from ZnO: Ga films features the degeneracy of semiconductor, which helps to recognize the enhancing of transparency and conductivity of ZnO films fabricated by AP-MOCVD using Ga-doping technique. (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3212895]
Interfacial Charge Carrier Dynamics in Core-Shell Au-CdS Nanocrystals
(2010-07-08)
Yang, Ting-Ting
;
Chen, Wei-Ta
;
Hsu, Yung-Jung
;
Wei, Kung-Hwa
;
Lin, Tai-Yuan
The interfacial charge carrier dynamics for core-shell Au-CdS nanocrystals with various shell thicknesses were investigated and presented. Due to the difference in band structures between Au and CdS, a pronounced photoinduced charge separation took place at the interface of Au and CdS, resulting in the electron-charged Au core and the hole-enriched CdS shell. The electron-charging of Au core in Au-CdS nanocrystals was revealed with the corresponding XPS analysis and photocurrent measurement. Time-resolved PL spectra were measured to quantitatively analyze the electron transfer event between CdS shell and Au core for Au-CdS nanocrystals. An increase in the electron-transfer rate constant was observed for Au-CdS nanocrystals with increasing shell thickness, probably due to the less pronounced electron hole interaction of thicker CdS, which enabled a fuller extent of participation of photoexcited electrons in the charge separation process. On the other hand, the hole-enriched CdS shell of Au-CdS nanocrystals upon light illumination was characterized with a photocatalytic process. The photocatalytic activity of Au-CdS nanocrystals was found to increase with increasing shell thickness, attributable to the greater capability of light absorption achieved by the extensive growth of the CdS shell. The correlation of photocatalytic activity with the shell thickness of Au-CdS nanocrystals corresponded well with that of the electron-transfer rate constant. As compared to the relevant commercial products like N-doped P-25 TiO(2), and CdS powders, the as-synthesized Au-CdS nanocrystals,exhibited superior photocatalytic performance under visible light illumination, demonstrating their potential as an effective visible-light-driven photocatalyst. Furthermore, the result of performance evaluation under natural sunlight shows that the present Au-CdS nanocrystals can be used as highly efficient photocatalysts which may practically harvest energy from sunlight.
Intrinsic p-type ZnO films fabricated by atmospheric pressure metal organic chemical vapor deposition
(2010-11-01)
Huang, Yen-Chin
;
Li, Zhen-Yu
;
Weng, Li-Wei
;
Uen, Wu-Yih
;
Lan, Shan-Ming
The structural, electrical, and optical properties of ZnO films fabricated by atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD) under various gas flow ratios of [H(2)O]/[DEZn] (VI/II ratio) ranging from 0.55 to 2.74 were systematically examined. Hall effect measurements exhibited an evident effect of the VI/II ratio on the conduction type of the intrinsic films. An n-type film was fabricated at the VI/II ratio=0.55; however, p-type ZnO films with the hole concentration of the order of 10(17) cm(-3) could be achieved at VI/II ratios higher than 1.0. In particular, the highest mobility of 91.6 cm(2)/V s and the lowest resistivity of 0.369 Omega cm have been achieved for the specimen fabricated at the VI/II ratio=1.10. Moreover, room-temperature photoluminescence (PL) measurements demonstrated an interstitial Zn (Zn(i)) donor defect related emission at 2.9 eV for the n-type film, while a Zn vacancy (V(Zn)) acceptor defect related one at 3.09 eV for the p-type films. The existence of material intrinsic defects was further confirmed by low temperature PL measurements conducted at 10 K. Conclusively, the conduction type of undoped ZnO films deposited by AP-MOCVD is resolved by the VI/II ratio used, which causes the formation of various kinds of intrinsic defects, Zn(i) otherwise VZn. p-type ZnO films with the hole concentration in the range of (1.5-3.3) x 10(17) cm(-3) can be achieved with good reproducibility by modulating a VI/II ratio the range 1.0-2.2 for the AP-MOCVD process. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3484138]
Low operation voltage macromolecular composite memory assisted by graphene nanoflakes
(2013)
Lai, Ying-Chih
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Wang, Di-Yan
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Huang, I-Sheng
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Chen, Yu-Ting
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Hsu, Yung-Hsuan
The trend towards simple and low-cost processing is one of the most important for macromolecular memory development. Here, bistable memory devices using a solution-processable active material, a mixture of graphene nanoflakes (GNFs) and insulating poly(vinyl alcohol) (PVA), are investigated, which serve as the first example for the direct integration of as-prepared nanoscale graphene into macromolecular memory devices through a one-step low-temperature processing method. Bistable electrical switching behavior and nonvolatile rewritable memory effects are realized by using an indium-tin-oxide/GNF-PVA/silver (ITO/GNF-PVA/Ag) sandwich structure. The resulting device exhibits low operation voltages of +1.4 V (turn-on) and -1.3 V (turn-off), which is promising for memory cells with low power consumptions. The programmable ON- and OFF-states possess a retention time of over 10(4) s and endure up to 10(7) read pulses. The carrier transport in the OFF- and ON-states follows the typical trap-limited space charge limited current and Ohmic laws, respectively. The asymmetric electrical switch behavior is therefore attributed to conducting filaments formed in the PVA layer assisted by the charged GNFs that induce the transition of the conductivity. Our study provides a potential approach for integrating as-prepared graphene into macromolecular memory devices with excellent performances through a simple solution-process.
Novel surface treatment film of polarizer to improve optical properties of 32 inch OCB mode LCD TV
(2007-01-01)
Lien, Jan-Tien
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Chen, Sze-Fen F.
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Pan, Chien-Lin
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Chang, Chih-Chun
;
Lin, Tai-Yuan
We have developed OCB mode LCD panel possess fast response time (Gray to Gray Level) about 0.98 ms and low color washout Gamma Distortion Index (D value) is 0.06, and it's smaller than VA mode LCD. To use novel surface-treatment film of polarizers is useful to reduce Chroma difference (Delta Cu'v') of horizontal viewing direction and increase viewing angles of 32 inch OCB panel. The value of Delta Cu'v' is lower than 0.02.
Photocatalytic effect of anodic titanium oxide nanotubes on various cell culture media
(2011-02-01)
Yu, Chun-Kang
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Hu, Kan-Hung
;
Wang, Shing-Hoa
;
Hsu, Todd
;
Tsai, Huei-Ting
The use of titanium dioxide (TiO(2)) in photodynamic therapy for the treatment of cancer cells has been proposed following studies of cultured cancer cells. In this work, an ordered channel array of anodic titanium oxide (ATO) was fabricated by anodizing titanium foil. The ATO layer of nanotubes with diameters of 100 nm was made in NH(4)F electrolyte by anodization. The photocatalytic effect of ATO was examined on various culture media by ultraviolet A (UV-A) (366 nm) irradiation. After UV-A irradiation of the ATO layer, redox potential of Tris-HCl buffer (pH 7.5) and dilute acrylamide solution increased instantaneously. The redox potential of the serum-containing RPMI1640 medium also increased dramatically, while that of serum-containing MEM and DMEM media increased slightly. The UVA-induced high redox potential was correlated with the greater ability to break down plasmid DNA strands. These phenomena suggest that a culture medium, such as RPMI1640, with a greater ability to produce free radical may be associated with a stronger photocatalytic effect of ATO on cultured cancer cells reported previously.
Plasmonic Carbon-Dot-Decorated Nanostructured Semiconductors for Efficient and Tunable Random Laser Action
(2018-01-01)
Liao, Wei-Cheng
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Liao, Yu-Ming
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Su, Chuan-Tsung
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Perumal, Packiyaraj
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Lin, Shih-Yao
Carbon dots have emerged as popular materials in various research fields, including biological and photovoltaic areas, while significant reports are lacking related to their applications in laser devices, which play a significant role in our daily life. In this work, we demonstrate the first controllable random laser assisted by the surface plasmon effect of carbon dots. Briefly, carbon dots derived from candle soot are randomly deposited on the surface of gallium nitride (GaN) nanorods to enhance the ultraviolet fluorescence of GaN and generate plasmonically enhanced random laser action with coherent feedback. Furthermore, potentially useful functionalities of tunable lasing threshold and controllable optical modes are achieved by adjusting the numbers of carbon dots, enabling applications in optical communication and identification technologies. In addition to providing an efficient alternative for plasmonically enhanced random laser devices with simple fabrication and low cost, our work also paves a useful route for the application of environmentally friendly carbon dots in optoelectronic devices.
Slanted n-ZnO/p-GaN nanorod arrays light-emitting diodes grown by oblique-angle deposition
(2014-05-01)
Lee, Ya-Ju
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Yang, Zu-Po
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Lo, Fang-Yuh
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Siao, Jhih-Jhong
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Xie, Zhong-Han
High-efficient ZnO-based nanorod array light-emitting diodes (LEDs) were grown by an oblique-angle deposition scheme. Due to the shadowing effect, the inclined ZnO vapor-flow was selectively deposited on the tip surfaces of pre-fabricated p-GaN nanorod arrays, resulting in the formation of nanosized heterojunctions. The LED architecture composed of the slanted n-ZnO film on p-GaN nanorod arrays exhibits a well-behaving current rectification of junction diode with low turn-on voltage of 4.7 V, and stably emits bluish-white luminescence with dominant peak of 390 nm under the operation of forward injection currents. In general, as the device fabrication does not involve passivation of using a polymer or sophisticated material growth techniques, the revealed scheme might be readily applied on other kinds of nanoscale optoelectronic devices. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
Ultrahigh-Performance Self-Powered Flexible Photodetector Driven from Photogating, Piezo-Phototronic, and Ferroelectric Effects
(1970-01-01)
Shen, Tien-Lin
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Chu, Yu-Wei
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Liao, Yu-Kuang
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Lee, Wen-Ya
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Kuo, Hao-Chung
Owing to the need for dynamic, real-time, and on-site data collection in internet of things applications, the realization of ultra-sensitive sensing networks with self-powered, flexible, and lightweight devices has become an important issue for the development of sensor systems. In this work, a novel, high-performance, self-powered photodetector is achieved through the combination of photogating, piezo-phototronic, and ferroelectric effect by incorporating a ferroelectric thin film of poly(vinylidene fluoride-co-trifluoroethylene) in a rationally designed device structure with suitable band alignment, which can modulate carrier transport behavior at the interface due to the internal electric field produced by light illumination, external strain, or voltage-poled dipole. This enables photocurrent and overall device performance to improve significantly. The unprecedented photodetector presented in this study has several merits, including mechanical flexibility and light weight that allow it to adapt to arbitrary surface topology; additionally, its self-powering capability and high reliability are urgently needed for the demanding functionality of devices for the development of next-generation optoelectronic devices, spanning from wearable communication to unattended harsh environments with a human-friendly interface.