Browsing by Author "Tien, Ching-Ho"

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Effect of the Phosphor Permanent Substrate on the Angular CCT for White Thin-Film Flip-Chip Light-Emitting Diodes
(2016-10)
Tien, Ching-Ho
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Ho, Kuo-Wei
;
Chien, Huan-Yu
;
Wuu, Dong-Sing
;
Horng, Ray-Hua
This paper developed a phosphor layer applied for thin-film flip-chip light-emitting diodes (TFFC-LEDs) to produce uniform phosphor-converted TFFC white LEDs (TFFC-WLEDs) by combination of laser liftoff, secondary transferring, and surface roughening process. The spin-coating method was used for phosphor layer fabrication onto a substrate to form the phosphor permanent substrate. The TFFC-LEDs were then bonded onto the permanent substrate. From the results, the blue TFFC GaN-based LED with roughened u-GaN surface on a glass substrate (TFRG-LED) demonstrated a 54.2% (at 350 mA) enhancement in light output power, compared with a blue flip-chip GaN-on-sapphire based LED. As the TFFC GaN/phosphor-/glass-based white LED with roughened u-GaN surface (TFRG-WLED) was operated at a forward-bias current of 350 mA, the enhancement of luminous flux was increased by 75.5%, compared with a TFFC GaN/phosphor template-/glass-based white LED. The angular correlated color temperature (CCT) deviation of a TFRG-WLED can be reduced to 1279 K in the range from -75 degrees to +75 degrees at 5000-6000 K application. The TFRG-WLED was fabricated on the glass substrate with the roughened u-GaN surface and the structure of phosphor layer closed to the u-GaN. These kinds of FRGB-WLED structure contribute to a better light extraction characteristic and a higher CCT stability.
Effect of Washing Solvents on the Properties of Air-Synthesized Perovskite CsPbBr3 Quantum Dots for Quantum Dot-Based Light-Emitting Devices
(2020-01-01)
Chen, Lung-Chien
;
Tien, Ching-Ho
;
Tseng, Po-Wei
;
Tseng, Zong-Liang
;
Huang, Wei-Lun
In order to improve the stability and cost of perovskite CsPbBr3 and establish a preparation process for quantum dot materials with excellent luminescence properties, CsPbBr3 quantum dots were synthesized by the hot injection method and the ice bath method in air ambient. Then, a proprietary purification system was used to improve the properties of the quantum dots and prepare high-quality perovskite quantum dot films. Optimal material and light characteristics were exhibited with ethyl acetate:hexane as the purification solvent. In the solution form, the photoluminescence wavelength could be maintained at 508 nm with almost no shift compared with other conditions, and the quantum yield could reach 99%; however, superior performance was obtained in the thin-film form, which exhibited little to no shift in the photoluminescence wavelength and, surprisingly, achieved a quantum yield of 91.6% with a narrow PL emission with a full width at half-maximum of 28 nm. In addition, exceptional thin-film uniformity was observed from scanning electron microscopy image analyses. The CsPbBr3 quantum dot light-emitting diode purified with ethyl acetate:hexane demonstrated an open-circuit voltage of 4 V, a maximum luminous brightness of 488 cd m(-2), and a maximum external quantum efficiency of 0.14%.
High-Uniformity Planar Mini-Chip-Scale Packaged LEDs with Quantum Dot Converter for White Light Source
(2019-05-29)
Chen, Lung-Chien
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Tien, Ching-Ho
;
Chen, De-Fu
;
Ye, Zhi-Ting
;
Kuo, Hao-Chung
This study proposes a novel direct-lit mini-chip-scale packaged light-emitting diode (mini-CSPLED) backlight unit (BLU) that used quantum dot (QD) film, diffusion plate, and two prism films to improve brightness uniformity. Three different luminous intensity units, 120 degrees mini-CSPLED, 150 degrees mini-CSPLED, and 180 degrees mini-CSPLED with different emission angle structures were fabricated using a CSP process. In terms of component characteristics, although the 180 degrees mini-CSPLED light output power is about loss 4% (at 10mA) compared with 150 degrees mini-CSPLED, it has a large emission angle that forms a planar light source that contributes to improving the BLU brightness uniformity and reduced quantity of LEDs at the same area. In terms of BLU analysis, the blue mini-CSPLEDs with different emission angles excite the different QD film thicknesses; the chromaticity coordinates conversion to the white light region. The BLU brightness increases as the QD film thickness increases from 60, 90, and 150m. This result can achieve a brightness uniformity of 86% in a 180 degrees mini-CSPLED BLU + 150-m-thick QD films as compared to the 120 degrees mini-CSPLED BLU and 150 degrees mini-CSPLED BLU.
Improved Optoelectronic Performance of High-Voltage Ultraviolet Light-Emitting Diodes Through Electrode Designs
(2017-11-01)
Tien, Ching-Ho
;
Kuo, Chen-Hao
;
Wuu, Dong-Sing
;
Horng, Ray-Hua
;
電子工程學系及電子研究所
High-efficiency high-voltage ultraviolet light-emitting diodes (HV-UVLEDs) consisting of a 4 x 4 microcells array with an area of 61 mil x 33 mil were designed and fabricated via the electrode pattern and interconnect technique. Polymer material was used to fill trench with planarization, and interconnection technology was used for metal layer connection to address wiring defect issue. In comparison with the conventional lateral UV-LED (C-UVLED), which had 33.6% and 34.7% enhancement in the light output power and wall-plug efficiency (at 1.5 W) of the HV-UVLEDs. A 56% improvement in the external quantum efficiency droop behavior was achieved for the HV-UVLEDs when compared with that of C-UVLED. This improvement can be attributed to superior current spreading in the HV-UVLED due to its smaller microcells, which increases light-emission efficiency overall.
ITO/nano-Ag Plasmonic Window Applied for Efficiency Improvement of Near-Ultraviolet Light Emitting Diodes
(2016)
Tien, Ching-Ho
;
Zhang, Chia-Hao
;
Chung, Shih-Hao
;
Ou, Shih-Liang
;
Horng, Ray-Hua
Performance of GaN-based light-emitting diodes fabricated using GaN epilayers grown on silicon substrates
(2014-01-13)
Horng, Ray-Hua
;
Wu, Bing-Rui
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Tien, Ching-Ho
;
Ou, Sin-Liang
;
Yang, Min-Hao
Light extraction of GaN-based light-emitting diodes grown on Si(111) substrate (GaN-on-Si based LEDs) is presented in this study. Three different designs of GaN-on-Si based LEDs with the lateral structure, lateral structure on mirror/Si(100) substrate, and vertical structure on mirror/Si(100) substrate were epitaxially grown by metalorganic chemical vapor deposition and fabricated using chemical lift-off and double-transfer techniques. Current-voltage, light output power, far-field radiation patterns, and electroluminescence characteristics of these three LEDs were discussed. At an injection current of 700 mA, the output powers of LEDs with the lateral structure on mirror/Si(100) substrate and vertical structure on mirror/Si(100) substrate were measured to be 155.07 and 261.07 mW, respectively. The output powers of these two LEDs had 70.63% and 187.26% enhancement compared to that of LED with the lateral structure, respectively. The result indicated this vertical structure LED was useful in improving the light extraction due to an enhancement in light scattering efficiency while the high-reflection mirror and diffuse surfaces were employed. (C) 2014 Optical Society of America
Perovskite CsPbBr3 Quantum Dots Prepared Using Discarded Lead-Acid Battery Recycled Waste
(2019-03-02)
Chen, Lung-Chien
;
Tien, Ching-Ho
;
Ou, Sin-Liang
;
Lee, Kun-Yi
;
Tian, Jianjun
Perovskite CsPbBr3 quantum dot (CsPbBr3-QD) recovery was performed using lead scrap from lead storage batteries. The perovskite CsPbBr3-QD characteristics were analyzed using different PbO/recycled PbO2 ratios. Scanning electron microscopy (SEM) was used to observe the film surface morphology and cross-section. High-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) were used to observe the perovskite CsPbBr3-QDs' structural characteristics. A photoluminescence (PL) measurement system was used to analyze the optical properties. The results show that lead scrap from lead-acid batteries as a material for perovskite CsPbBr3-QD production can be successfully synthesized. This saves material and also proves that recycling is valuable. The proposed approach is helpful for future material shortages and materials not easily accessible. Although the efficiency is not very high, this process will be purified using recycled lead in the future to achieve higher quantum yield.