Browsing by Author "Sher, Chin-Wei"

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A critical review on two-dimensional quantum dots (2D QDs): From synthesis toward applications in energy and optoelectronics
(2019-11-01)
Manikandan, Arumugam
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Chen, Yu-Ze
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Shen, Chih-Chiang
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Sher, Chin-Wei
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Kuo, Hao-Chung
Recent advances in the development of quantum dots (QDs) have offered new possibilities for the exploration of sensors, bio imaging, batteries, electrochemical water splitting and optoelectronic applications because of their intriguing optical, electrical, catalytic and electrochemical properties. Among QDs, atomically thin two-dimensional quantum dots (2D QDs) derived from graphene sheets, transition metal dichalcogenide (TMD) layers and phosphorene have been of considerable interest for the past few years. There have been several intensive studies of carbon QDs, but TMD QDs and heterostructures based on 2D QDs are rapidly advancing. Herein, the synthesis and properties of 2D QDs, particularly carbon and TMD QDs, are reviewed for the recent progress in their application toward electrochemical water splitting, photocatalytic wastewater treatment, supercapacitors, batteries and photodetectors. Moreover, the assembly of such 2D QDs to achieve industrial-scale production and boost their performance in widespread applications is emphasized.
A high quality liquid-type quantum dot white light-emitting diode
(2016-01-01)
Sher, Chin-Wei
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Lin, Chin-Hao
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Lin, Huang-Yu
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Lin, Chien-Chung
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Huang, Che-Hsuan
This study demonstrates a novel package design to store colloidal quantum dots in liquid format and integrate them with a standard LED. The high efficiency and high quality color performance at a neutral white correlated color temperature is demonstrated. The experimental results indicate that the liquid-type quantum dot white light-emitting diode (LQD WLED) is highly efficient and reliable. The luminous efficiency and color rendering index (CRI) of the LQD WLED can reach 271 lm W-op(-1) and 95, respectively. Moreover, a glass box is employed to prevent humidity and oxygen erosion. With this encapsulation design, our quantum dot box can survive over 1000 hours of storage time.
A high quality liquid-type quantum dot white light-emitting diode (vol 8, pg 1117, 2016)
(2018-04-07)
Sher, Chin-Wei
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Lin, Chih-Hao
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Lin, Huang-Yu
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Lin, Chien-Chung
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Huang, Che-Hsuan
Design and Fabrication of the Reliable GaN Based Vertical-Cavity Surface-Emitting Laser via Tunnel Junction
(2019-04-01)
Shen, Chih-Chiang
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Lu, Yun-Ting
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Yeh, Yen-Wei
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Chen, Cheng-Yuan
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Chen, Yu-Tzu
In this study, we theoretically designed and experimentally fabricated an InGaN vertical-cavity surface-emitting laser (VCSEL) with a tunnel junction (TJ) structure. From numerical simulation results, the optical loss of the device can be reduced by a TJ structure. Additionally, the leakage current of the VCSEL with TJ structure was much smaller than that of the VCSEL with an Indium-Tin-Oxide (ITO) layer. We have been demonstrated that laser output performance is improved by using the TJ structure when compared to the typical VCSEL structure of the ITO layer. The output power obtained at 2.1 mW was enhanced by a factor of 3.5 by the successful reduction of threshold current density (J(th)) from 12 to 8.5 kA/cm(2), and the enlarged slope efficiency was due to less absorption in VCSEL with a TJ structure. Finally, the samples passed the high temperature (70 degrees C) and high operation current (1.5 x J(th)) test for over 500 h.
Fabrication of Flexible White Light-Emitting Diodes from Photoluminescent Polymer Materials with Excellent Color Quality
(2017-10-11)
Lin, Huang-Yu
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Sher, Chin-Wei
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Lin, Chih-Hao
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Tu, Hsien-Hao
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Chen, Xin Yin
This study developed flexible light-emitting diodes (LEDs) with warm white and neutral white light. A simple ultraviolet flip-chip sticking process was adopted for the pumping source and combined with polymer and quantum dot (QD) films technology to yield white light. The polymer-blended flexible LEDs exhibited higher luminous efficiency than the QD-blended flexible LEDs. Moreover, the polymer-blended LEDs, achieved excellent color-rendering index (CRI) values (Ra = 96 and R9 = 96), with high reliability, demonstrating high suitability for special applications like accent, down, or retrofit lights in the future. In places such as a museum, kitchen, or surgery room, its high R9 and high CRI characteristics can provide high-quality services.
Full-color monolithic hybrid quantum dot nanoring micro light-emitting diodes with improved efficiency using atomic layer deposition and nonradiative resonant energy transfer
(2019-04-01)
Chen, Sung-Wen Huang
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Shen, Chih-Chiang
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Wu, Tingzhu
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Liao, Zhen-You
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Chen, Lee-Feng
Full-color displays based on micro light-emitting diodes (mu LEDs) can be fabricated on monolithic epitaxial wafers. Nanoring (NR) structures were fabricated on a green LED epitaxial wafer; the color of NR-mu LEDs was tuned from green to blue through strain relaxation. An Al2O3 layer was deposited on the sidewall of NR-mu LEDs, which improved the photoluminescence intensity by 143.7%. Coupling with the exposed multiple quantum wells through nonradiative resonant energy transfer, red quantum dots were printed to NR-mu LEDs for a full-color display. To further improve the color purity of the red light, a distributed Bragg reflector is developed to reuse the excitation light. (C) 2019 Chinese Laser Press
Giant Optical Anisotropy of Perovskite Nanowire Array Films
(1970-01-01)
Lin, Chun-Ho
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Kang, Chieh-Yu
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Wu, Ting-Zhu
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Tsai, Chun-Lin
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Sher, Chin-Wei
Polarizers play a key role in generating polarized light for display, imaging, and data communication, but adoption often suffers from high optical loss. Recently, due to superior optoelectronic properties, halide perovskites have been widely developed for lighting applications; however, highly polarized emission (polarization degree >0.8) has not yet been realized with perovskites. Herein, by incorporating inkjet printing and an anodic aluminum oxide (AAO) confinement strategy, highly ordered perovskite nanowire (NW) arrays are demonstrated for anisotropic optical applications. The optical device based on perovskite NW arrays reveals a high photoluminescence external quantum efficiency of 21.6% and emits highly polarized light with polarization degree up to 0.84. The highly polarized emission from perovskite NW arrays has potential to considerably reduce the optical loss of polarizers, which may attract great interest in developing polarized light sources for next-generation optoelectronic applications.
Growth, transfer printing and colour conversion techniques towards full-colour micro-LED display
(2020-05-01)
Zhou, Xiaojie
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Tian, Pengfei
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Sher, Chin-Wei
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Wu, Jiang
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Liu, Hezhuang
Micro light-emitting diode (micro-LED) display, mainly based on inorganic GaN-based LED, is an emerging technique with high contrast, low power consumption, long lifetime and fast response time compared to liquid crystal display (LCD) and organic light-emitting diode (OLED) display. Therefore, many research institutes and companies have conducted in-depth research on micro-LED in the full-colour display, gradually realizing the commercialization of micro-LED. And the current research results of micro-LED indicate that it can be widely used in display, visible light communication (VLC), biomedicine and other fields. Although micro-LED has broad commercial prospects, it still faces great challenges, such as the effect of size reduction on performance, the realization of high-density integration on a single wafer for independent addressing of full-colour micro-LED display, the improvement of repair technique and yield a al. This paper reviews the key solutions to the technical difficulties of the full-colour micro-LED display. Specifically, this review analyzes and discusses a variety of advanced full-colour micro-LED display techniques with a focus on three aspects: growth technique, transfer printing technique and colour conversion technique. This review demonstrates the opportunities, progress and challenges of these techniques, aiming to guide the development of full-colour micro-LED display.
Highly Efficient and Stable White Light-Emitting Diodes Using Perovskite Quantum Dot Paper
(1970-01-01)
Kong, Chieh-Yu
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Lin, Chun-Ho
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Lin, Chih-Hao
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Li, Ting-You
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Chen, Sung-Wen Huang
Perovskite quantum dots (PQDs) are a competitive candidate for next-generation display technologies as a result of their superior photoluminescence, narrow emission, high quantum yield, and color tunability. However, due to poor thermal resistance and instability under high energy radiation, most PQD-based white light-emitting diodes (LEDs) show only modest luminous efficiency of approximate to 50 lm W-1 and a short lifetime of <100 h. In this study, by incorporating cellulose nanocrystals, a new type of QD film is fabricated: CH3NH3PbBr3 PQD paper that features 91% optical absorption, intense green light emission (518 nm), and excellent stability attributed to the complexation effect between the nanocellulose and PQDs. The PQD paper is combined with red K2SiF6:Mn4(+) phosphor and blue GaN LED chips to fabricate a high-performance white LED demonstrating ultrahigh luminous efficiency (124 lm W-1), wide color gamut (123% of National Television System Committee), and long operation lifetime (240 h), which paves the way for advanced lighting technology.
Hybrid-type white LEDs based on inorganic halide perovskite QDs: candidates for wide color gamut display backlights
(2019-05-01)
Lin, Chih-Hao
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Verma, Akta
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Kang, Chieh-Yu
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Pai, Yung-Min
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Chen, Tzu-Yu
We demonstrate inorganic halide perovskite quantum-dots-based white light-emitting diodes via three different geometries, including liquid, solid, and hybrid types. Problems of fast anion exchange and aggregation in the cases of liquid- and solid-type devices are discussed in detail and push us to move towards the fabrication of a hybrid-type device structure. The experiment results illustrate that a hybrid-type device has the highest luminance efficiency (51 lm/W) and a wide color gamut (122% of NTSC and 91% of Rec. 2020). Therefore, we conclude that a hybrid-type device can provide an outstanding color gamut for high color gamut display applications. (c) 2019 Chinese Laser Press
Large-area, uniform white light LED source on a flexible substrate
(2015-09-21)
Sher, Chin-Wei
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Chen, Kuo-Ju
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Lin, Chien-Chung
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Han, Hau-Vei
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Lin, Huang-Yu
This study demonstrates the flexible white LED structure with high lumen efficiency and uniform optical performance for neutral white and warm white CCT. Flip-chip LEDs were attached on a polyimide substrate with copper strips as electrical and thermal conduction paths. Yellow phosphors are mixed with polydimenthysiloxane (PDMS) to provide mechanical support and flexibility. The light efficiency of this device can reach 120 lm/W and 85% of light output uniformity of the emission area can be achieved. Moreover, the optical simulation is employed to evaluate various designs of this flexible film in order to obtain uniform output. Both the pitch between the individual devices and the thickness of the phosphor film are calculated for optimization purpose. This flexible white LED with high lumen efficiency and good reliability is suitable for the large area fixture in the general lighting applications. (C) 2015 Optical Society of America
Liquid Type Nontoxic Photoluminescent Nanomaterials for High Color Quality White-Light-Emitting Diode
(2018-12-22)
Lin, Chih-Hao
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Pai, Yung-Min
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Lee, Chun-Fu
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Verma, Akta
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Lin, Huang-Yu
High-brightness white-light-emitting diodes (w-LEDs) with excellent color quality is demonstrated by using nontoxic nanomaterials. Previously, we have reported the high color quality w-LEDs with heavy-metal phosphor and quantum dots (QDs), which may cause environmental hazards. In the present work, liquid-type white LEDs composed of nontoxic materials, named as graphene and porous silicon quantum dots are fabricated with a high color rendering index (CRI) value gain up to 95. The liquid-typed device structure possesses minimized surface temperature and 25% higher value of luminous efficiency as compare to dispensing-typed structure. Further, the as-prepared device is environment friendly and attributed to low toxicity. The low toxicity and high R9 (87) component values were conjectured to produce new or improve current methods toward bioimaging application.
Micro-light-emitting diodes with quantum dots in display technology
(2020-05-11)
Liu, Zhaojun
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Lin, Chun-Ho
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Hyun, Byung-Ryool
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Sher, Chin-Wei
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Lv, Zhijian
Micro-light-emitting diodes (mu-LEDs) are regarded as the cornerstone of next-generation display technology to meet the personalised demands of advanced applications, such as mobile phones, wearable watches, virtual/augmented reality, micro-projectors and ultrahigh-definition TVs. However, as the LED chip size shrinks to below 20 mu m, conventional phosphor colour conversion cannot present sufficient luminance and yield to support high-resolution displays due to the low absorption cross-section. The emergence of quantum dot (QD) materials is expected to fill this gap due to their remarkable photoluminescence, narrow bandwidth emission, colour tuneability, high quantum yield and nanoscale size, providing a powerful full-colour solution for mu-LED displays. Here, we comprehensively review the latest progress concerning the implementation of mu-LEDs and QDs in display technology, including mu-LED design and fabrication, large-scale mu-LED transfer and QD full-colour strategy. Outlooks on QD stability, patterning and deposition and challenges of mu-LED displays are also provided. Finally, we discuss the advanced applications of QD-based mu-LED displays, showing the bright future of this technology. Micro-LEDs: A fine display by quantum dots Micrometre-sized light-emitting diodes (LEDs) based on quantum dots (QDs) will propel the next generation of display technologies, a review by leading researchers shows. Conventional LED designs, with phosphor coatings that convert light to different colours, are difficult to make smaller than 20 micrometres. Jr-Hau He at City University of Hong Kong and co-workers explain how this problem can be tackled using QDs, tiny particles whose optical properties can be tuned by varying their size, providing brighter and more precise colours. Ultra-high-resolution displays based on phospholuminescent QD-LEDs are now being released to the market thanks to finely-controlled methods for synthesising QDs and depositing them onto films. Further research should focus on the best ways to stabilise and protect QD films within LEDs, and to continue developing electroluminescent QD-LEDs, which could potentially outperform their phospholuminescent cousins.
Mini-LED and Micro-LED: Promising Candidates for the Next Generation Display Technology
(2018-09-01)
Wu, Tingzhu
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Sher, Chin-Wei
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Lin, Yue
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Lee, Chun-Fu
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Liang, Shijie
Displays based on inorganic light-emitting diodes (LED) are considered as the most promising one among the display technologies for the next-generation. The chip for LED display bears similar features to those currently in use for general lighting, but it size is shrunk to below 200 microns. Thus, the advantages of high efficiency and long life span of conventional LED chips are inherited by miniaturized ones. As the size gets smaller, the resolution enhances, but at the expense of elevating the complexity of fabrication. In this review, we introduce two sorts of inorganic LED displays, namely relatively large and small varieties. The mini-LEDs with chip sizes ranging from 100 to 200 m have already been commercialized for backlight sources in consumer electronics applications. The realized local diming can greatly improve the contrast ratio at relatively low energy consumptions. The micro-LEDs with chip size less than 100 m, still remain in the laboratory. The full-color solution, one of the key technologies along with its three main components, red, green, and blue chips, as well color conversion, and optical lens synthesis, are introduced in detail. Moreover, this review provides an account for contemporary technologies as well as a clear view of inorganic and miniaturized LED displays for the display community.
Novel Method for Estimating Phosphor Conversion Efficiency of Light-Emitting Diodes
(2018-12-01)
Lin, Chih-Hao
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Huang, Che-Hsuan
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Pai, Yung-Min
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Lee, Chung-Fu
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Lin, Chien-Chung
This study presents a novel method for estimating the phosphor conversion efficiency of white light-emitting diodes (WLEDs) with different ratios of phosphors. Numerous attempts have been made for predicting the phosphor conversion efficiency of WLEDs using Monte Carlo ray tracing and the Mie scattering theory. However, because efficiency depends on the phosphor concentration, obtaining a tight match between this model and the experimental results remains a major challenge. An accurate prediction depends on various parameters, including particle size, morphology, and packaging process criteria. Therefore, we developed an efficient model that can successfully correlate the total absorption ratio to the phosphor concentration using a simple equation for estimating the spectra and lumen output. The novel and efficient method proposed here can accelerate WLED development by reducing costs and saving fabrication time.
Optical cross-talk reduction in a quantum-dot-based full-color micro-light-emitting-diode display by a lithographic-fabricated photoresist mold
(2017-10-01)
Lin, Huang-Yu
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Sher, Chin-Wei
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Hsieh, Dan-Hua
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Chen, Xin-Yin
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Chen, Huang-Ming Philip
In this study, a full-color emission red-green-blue (RGB) quantum-dot (QD)-based micro-light-emitting-diode (micro-LED) array with the reduced optical cross-talk effect by a photoresist mold has been demonstrated. The UV micro-LED array is used as an efficient excitation source for the QDs. The aerosol jet technique provides a narrow linewidth on the micrometer scale for a precise jet of QDs on the micro-LEDs. To reduce the optical cross-talk effect, a simple lithography method and photoresist are used to fabricate the mold, which consists of a window for QD jetting and a blocking wall for cross-talk reduction. The cross-talk effect of the well-confined QDs in the window is confirmed by a fluorescence microscope, which shows clear separation between QD pixels. A distributed Bragg reflector is covered on the micro-LED array and the QDs' jetted mold to further increase the reuse of UV light. The enhanced light emission of the QDs is 5%, 32%, and 23% for blue, green, and red QDs, respectively. (C) 2017 Chinese Laser Press
Patterned structure of REMOTE PHOSPHOR for phosphor-converted white LEDs
(2011-07-04)
Kuo, Hao-Chung
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Hung, Cheng-Wei
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Chen, Hsin-Chu
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Chen, Kuo-Ju
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Wang, Chao-Hsun
High efficiency white light-emitting diodes with superior color-mixing have been investigated. It is suggested that the patterned remote phosphor structure could improve the uniformity of angular-dependent correlated color temperature (CCT) and achieve high chromatic stability in wider operating current range, as compared to the conventional remote phosphor coating structure. In this experiment, we employed a pulse spray coating method to place the patterned phosphor on the package and to leave a window region. The window area, a clear space without coating of the phosphor not only increases the extraction efficiency of blue rays at large angle, but also improves the stability of angular-dependent CCT. Moreover, the CCT deviation could be reduced from 1320 K to 266 K by this patterned remote phosphor method, and the stray blue/yellow light within the package can be effectively reduced and controlled. The design was verified both experimentally and theoretically. (C) 2011 Optical Society of America
Square Column Structure of High Efficiency, Reliable, Uniformly Flexible LED Devices
(2018-12-01)
Lin, Chih-Hao
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Pai, Yung-Min
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Kang, Chieh-Yu
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Lin, Huang-Yu
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Lee, Chun-Fu
This study demonstrates that flexible white LEDs, doped with diffusion particles and with a square column structure, have excellent luminosity, uniformity, and bending reliability. This large area (5 cm x 5 cm) square column flexible device had a smaller thickness (2 mm), and enhancements in both luminous efficiency (29.5%) and uniformity (44.6%) compared to the characteristics of the 6 mm reference sample. Optimization of the reflective layer coating for the square column, flexible white LED was achieved with a higher luminous efficiency (171 lm/w) and uniformity (92%). We designed a novel lightning bolt electrode to improve reliability and bendability. After the bending test, the blue flexible LED had a lower bending diameter (10 mm) but more bending circles (increased to 2000 times.
Ultra-High Light Extraction Efficiency and Ultra-Thin Mini-LED Solution by Freeform Surface Chip Scale Package Array
(2019-04-01)
Huang, Che-Hsuan
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Kang, Chieh-Yu
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Chang, Shu-Hsiu
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Lin, Chih-Hao
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Lin, Chun-Yu
In this study, we present a novel type of package, freeform-designed chip scale package (FDCSP), which has ultra-high light extraction efficiency and bat-wing light field. For the backlight application, mainstream solutions are chip-scale package (CSP) and surface-mount device package (SMD). Comparing with these two mainstream types of package, the light extraction efficiency of CSP, SMD, and FDCSP are 88%, 60%, and 96%, respectively. In addition to ultra-high light extraction efficiency, because of the 160-degree bat-wing light field, FDCSP could provide a thinner and low power consumption mini-LED solution with a smaller number of LEDs than CSP and SMD light source array.
Ultrawide Color Gamut Perovskite and CdSe/ZnS Quantum-Dots-Based White Light-Emitting Diode with High Luminous Efficiency
(2019-09-01)
Lin, Chih-Hao
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Kang, Chieh-Yu
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Verma, Akta
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Wu, Tingzhu
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Pai, Yung-Min
We demonstrate excellent color quality of liquid-type white light-emitting diodes (WLEDs) using a combination of green light-emitting CsPbBr3 and red light-emitting CdSe/ZnS quantum dots (QDs). Previously, we reported red (CsPbBr1.2I1.8) and green (CsPbBr3) perovskite QDs (PQDs)-based WLEDs with high color gamut, which manifested fast anion exchange and stability issues. Herein, the replacement of red PQDs with CdSe/ZnS QDs has resolved the aforementioned problems effectively and improved both stability and efficiency. Further, the proposed liquid-type device possesses outstanding color gamut performance (132% of National Television System Committee and 99% of Rec. 2020). It also shows a high efficiency of 66 lm/W and an excellent long-term operation stability for over 1000 h.