Browsing by Author "Chen, Yang-Fang"

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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
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Jing, Ting-Shivan
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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.
Color-conversion efficiency enhancement of quantum dots via selective area nano-rods light-emitting diodes
(2016-08-22)
Liu, Che-Yu
;
Chen, Tzu-Pei
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Kao, Tsung Sheng
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Huang, Jhih-Kai
;
Kuo, Hao-Chung
A large enhancement of color-conversion efficiency of colloidal quantum dots in light-emitting diodes (LEDs) with novel structures of nanorods embedded in microholes has been demonstrated. Via the integration of nano-imprint and photolithography technologies, nanorods structures can be fabricated at specific locations, generating functional nanostructured LEDs for high-efficiency performance. With the novel structured LED, the color-conversion efficiency of the existing quantum dots can be enhanced by up to 32.4%. The underlying mechanisms can be attributed to the enhanced light extraction and nonradiative energy transfer, characterized by conducting a series of electroluminescence and time-resolved photoluminescence measurements. This hybrid nanostructured device therefore exhibits a great potential for the application of multi-color lighting sources. (C) 2016 Optical Society of America
High-Efficiency InGaN/GaN Core-Shell Nanorod Light-Emitting Diodes With Low-Peak Blueshift and Efficiency Droop
(2017-03)
Tzou, An-Jye
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Hsieh, Dan-Hua
;
Hong, Kuo-Bin
;
Lin, Da-Wei
;
Huang, Jhih-Kai
In this study, novel three-dimensional (3-D) nanoscale structures and methodology are demonstrated for application in high-efficiency core-shell nanorod (NR) light-emitting diodes (LEDs). The key to our successful growth of the structures is the introduction of passivation, which can be used to selectively grow active layers in desired structures. Through the fabrication methodology, core-shell NR green LEDs exhibiting large nonpolar active region and homogeneous indium distributions without a point tip shape were achieved. Stable light emission at a central wavelength of 518 nm was achieved as the injected current increased to more than 40 mA. The improved NR LEDs exhibited a stable luminescence emission wavelength (blueshift of 62 nm) and low-efficiency droop (18.1%) at 200 mA. Our scheme is scalable and compatible with current technologies, which provides a new perspective for developing high-performance, 3-D nanoscale optoelectronic devices.
Hypericin-mediated selective photomodification of connective tissues
(2017-01-01)
Hovhannisyan, V.
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Hovhannisyan, A.
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Ghukasyan, V.
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Guo, H. W.
;
Chen, Y. F.
Hypericin (Hyp) has received attention due to its high phototoxicity against viruses and anti-tumor photoactivity. Using two-photon imaging, we demonstrated that Hyp induced photosensitized modification of collagen fibers in native tissues. Dynamics of photo-processes was monitored by time-lapse multiphoton imaging. We showed that Hyp-mediated processes in collagen tissues may be used for the selective modification of collagen fibers.
Intrinsic Ultralow-Threshold Laser Action from Rationally Molecular Design of Metal-Organic Framework Materials
(2020-08-12)
Bera, Krishna Prasad
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Kamal, Saqib
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Inamdar, Arif I.
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Sainbileg, Batjargal
;
Lin, Hung-, I
Metal-organic frameworks (MOFs) are superior for multiple applications including drug delivery, sensing, and gas storage because of their tunable physiochemical properties and fascinating architectures. Optoelectronic application of MOFs is difficult because of their porous geometry and conductivity issues. Recently, a few optoelectronic devices have been fabricated by a suitable design of integrating MOFs with other materials. However, demonstration of laser action arising from MOFs as intrinsic gain media still remains challenging, even though some studies endeavor on encapsulating luminescence organic laser dyes into the porous skeleton of MOFs to achieve laser action. Unfortunately, the aggregation of such unstable laser dyes causes photoluminescence quenching and energy loss, which limits their practical application. In this research, unprecedently, we demonstrated ultralow-threshold (similar to 13 nJ/cm(2)) MOF laser action by a judicious choice of metal nodes and organic linkers during synthesis of MOFs. Importantly, we also demonstrated that the white random lasing from the beautiful microflowers of organic linkers possesses a porous network, which is utilized to synthesize the MOFs. The highly luminescent broad-band organic linker 1,4-NDC, which itself exhibits a strong white random laser, is used not only to achieve the stimulated emission in MOFs but also to reduce the lasing threshold. Such white lasing has multiple applications from bioimaging to the recently developed versatile Li-Fi technology. In addition, we showed that the smooth facets of MOF microcrystals can show Fabry-Perot resonant cavities having a high quality factor of similar to 10(3) with excellent photostability. Our unique discovery of stable, nontoxic, high-performance MOF laser action will open up a new route for the development of new optoelectronic devices.
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.
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.
Purely Sidewall InGaN/GaN Core-Shell Nanorod Green Light-Emitting Diodes
(2015)
Lin, Da-Wei
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Wu, Yung-Chi
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Kuo, Hao-Chung
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Chi, Gou-Chung
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Hsu, Lung-Hsing
A novel purely sidewall InGaN/GaN core-shell nanorod green light-emitting diode (LED) has been demonstrated by 3D dielectric passivation and selective epitaxial growth technologies. The LED device exhibits unprecedented stable emission wavelength and low efficiency droop.
Seeing pressure in color based on integration o highly sensitive pressure sensor and emission tunable light emitting diode
(2019-11-25)
Shen, Tien-Lin
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Chen, Chien-Tung
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Liao, Yu-Kuang
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Su, Teng-Yu
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Liu, Che-Yu
We demonstrate a highly sensitive, low-cost, environmental-friendly pressure sensor derived from a wool-based pressure sensor with wide pressure sensing range using wool bricks embedded with a Ag nano-wires. The easy fabrication and light weight allow portable and wearable device applications. Wth the integration of a light-emitting diode possessing multi-wavelength emission, we illustrate a hybrid multi-functional LED-integrated pressure sensor that is able to convert different applied pressures to light emission with different wavelengths. Due to the high sensitivity of the pressure sensor, the demonstration of acoustic signal detection has also been presented using sound of a metronome and a speaker playing a song. This multi-functional pressure sensor can be implemented to technologies such as smart lighting, health care, visible light communication (VLC), and other internet of things (IoT) applications. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Self-Powered, Self-Healed, and Shape-Adaptive Ultraviolet Photodetectors
(2020-02-26)
Tsai, Meng-Shian
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Shen, Tien-Lin
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Wu, Hsing-Mei
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Liao, Yu-Ming
;
Liao, Yu-Kuang
The emergence of self-healing devices in recent years has drawn a great amount of attention in both academics and industry. Self-healed devices can autonomically restore a rupture as unexpected destruction occurs, which can efficiently prolong the life span of the devices; hence, they have an enhanced durability and decreased replacement cost. As a result, integration of wearable devices with self-healed electronics has become an indispensable issue in smart wearable devices. In this study, we present the first self-powered, self-healed, and wearable ultraviolet (UV) photodetector based on the integration of agarose/poly(vinyl alcohol) (PVA) double network (DN) hydrogels, which have the advantages of good mechanical strength, self-healing ability, and tolerability of multiple types of damage. With the integration of a DN hydrogel substrate, the photodetector enables 90% of the initial efficiency to be restored after five healing cycles, and each rapid healing time is suppressed to only 10 s. The proposed device has several merits, including having an all spray coating, self-sustainability, biocompatibility, good sensitivity, mechanical flexibility, and an outstanding healing ability, which are all essential to build smart electronic systems. The unprecedented self-healed photodetector expands the future scope of electronic skin design, and it also offers a new platform for the development of next-generation wearable electronics.
Tunable insulator-quantum Hall transition in a weakly interacting two-dimensional electron system
(2013-07-03)
Lo, Shun-Tsung
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Wang, Yi-Ting
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Lin, Sheng-Di
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Strasser, Gottfried
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Bird, Jonathan P.
We have performed low-temperature measurements on a gated two-dimensional electron system in which electron-electron (e-e) interactions are insignificant. At low magnetic fields, disorder-driven movement of the crossing of longitudinal and Hall resistivities (rho (xx) and rho (xy)) can be observed. Interestingly, by applying different gate voltages, we demonstrate that such a crossing at rho (xx) similar to rho (xy) can occur at a magnetic field higher, lower, or equal to the temperature-independent point in rho (xx) which corresponds to the direct insulator-quantum Hall transition. We explicitly show that rho (xx) similar to rho (xy) occurs at the inverse of the classical Drude mobility 1/mu (D) rather than the crossing field corresponding to the insulator-quantum Hall transition. Moreover, we show that the background magnetoresistance can affect the transport properties of our device significantly. Thus, we suggest that great care must be taken when calculating the renormalized mobility caused by e-e interactions.
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.