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A special issue of Energies (ISSN 1996-1073).

Deadline for manuscript submissions: closed (15 September 2017) | Viewed by 40793

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Prof. Dr. Hsiang-Chen Wang

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Guest Editor

Graduate Institute of Opto-Mechatronics, National Chung Cheng University, 168 University Rd., Min-Hsiung, Chia-Yi 62102, Taiwan
Interests: biomedical science and engineering; biomedical sensors and images; hyperspectral imaging; optoelectronic semiconductor materials and devices; artificial intelligence
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Prof. Dr. Ya-Ju Lee

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Guest Editor

Institute of Electro-Optical Science and Technology, National Taiwan Normal University, No.88, Sec. 4, Ting-Chou Rd., Taipei 11677, Taiwan
Interests: optoelectronic semiconductor materials and devices; nano-fabrication process; green energy technology
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Special Issue Information

Dear Colleagues,

The Nobel Prize in Physics 2014 was awarded “for the invention of efficient blue light-emitting diodes which has enabled bright and energy-saving white light sources". Due to the fact that one fourth of electricity use in the world is for lighting, LED lights can contribute in vastly reducing energy usage in the world. Moreover, LED lights can be used for up to 100,000 hours, compared to 1000 hours for incandescent lights, and 10,000 hours of fluorescent lights, and, thus, can also greatly reduce resource costs. Progress in solid state lightings required innovations in devices and concepts in order to achieve energy-saving and environmental-protecting capabilities. In this Special Issue, the Guest Editors attempt to bring some of the recent technological advances in UV LEDs, micro-LED, QD-LED, blue laser, new materials, smart lighting, and color lighting with the goal of achieving energy-saving.

Prof. Dr. Hsiang-Chen Wang
Prof. Dr. Ya-Ju Lee
Guest Editors

Manuscript Submission Information

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Keywords

UV LEDs
micro-LED
QD-LED
blue laser
new materials
smart lighting
and color lighting

Published Papers (6 papers)

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Research

7652 KiB

Open AccessArticle

LED Uniform Illumination Using Double Linear Fresnel Lenses for Energy Saving

by Ngoc Hai Vu, Thanh Tuan Pham and Seoyong Shin

Energies 2017, 10(12), 2091; https://doi.org/10.3390/en10122091 - 11 Dec 2017

Cited by 17 | Viewed by 11594

Abstract

We present a linear Fresnel lens design for light-emitting diode (LED) uniform illumination applications. The LED source is an array of LEDs. An array of collimating lens is applied to collimate output from the LED array. Two linear Fresnel lenses are used to redistribute the collimated beam along two dimensions in the illumination area. Collimating lens and linear Fresnel lens surfaces are calculated by geometrical optics and nonimaging optics. The collimated beam output from the collimating lens array is divided into many fragments. Each fragment is refracted by a segment of Fresnel lens and distributed over the illumination area, so that the total beam can be distributed to the illumination target uniformly. The simulation results show that this design has a compact structure, high optical efficiency of 82% and good uniformity of 76.9%. Some consideration of the energy savings and optical performance are discussed by comparison with other typical light sources. The results show that our proposed LED lighting system can reduce energy consumption five-times in comparison to using a conventional fluorescent lamp. Our research is a strong candidate for low cost, energy savings for indoor and outdoor lighting applications. Full article

(This article belongs to the Special Issue Solid State Lighting)

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4023 KiB

Open AccessArticle

Magnetron Sputter Epitaxy of High-Quality GaN Nanorods on Functional and Cost-Effective Templates/Substrates

by Elena Alexandra Serban, Justinas Palisaitis, Muhammad Junaid, Lina Tengdelius, Hans Högberg, Lars Hultman, Per Ola Åke Persson, Jens Birch and Ching-Lien Hsiao

Energies 2017, 10(9), 1322; https://doi.org/10.3390/en10091322 - 02 Sep 2017

Cited by 23 | Viewed by 6285

Abstract

We demonstrate the versatility of magnetron sputter epitaxy by achieving high-quality GaN nanorods on different substrate/template combinations, specifically Si, SiC, TiN/Si, ZrB₂/Si, ZrB₂/SiC, Mo, and Ti. Growth temperature was optimized on Si, TiN/Si, and ZrB₂/Si, resulting in increased nanorod aspect ratio with temperature. All nanorods exhibit high purity and quality, proved by the strong bandedge emission recorded with cathodoluminescence spectroscopy at room temperature as well as transmission electron microscopy. These substrates/templates are affordable compared to many conventional substrates, and the direct deposition onto them eliminates cumbersome post-processing steps in device fabrication. Thus, magnetron sputter epitaxy offers an attractive alternative for simple and affordable fabrication in optoelectronic device technology. Full article

(This article belongs to the Special Issue Solid State Lighting)

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1031 KiB

Open AccessArticle

The Effect of Imbalanced Carrier Transport on the Efficiency Droop in GaInN-Based Blue and Green Light-Emitting Diodes

by Jun Hyuk Park, Jaehee Cho, E. Fred Schubert and Jong Kyu Kim

Energies 2017, 10(9), 1277; https://doi.org/10.3390/en10091277 - 27 Aug 2017

Cited by 14 | Viewed by 3880

Abstract

The effect of strongly-imbalanced carrier concentration and mobility on efficiency droop is studied by comparing the onset voltage of high injection, the onset current density of the droop, and the magnitude of the droop, as well as their temperature dependence, of GaInN-based blue and green light-emitting diodes (LEDs). An n-to-p asymmetry factor is defined as σn/σp, and was found to be 17.1 for blue LEDs and 50.1 for green LEDs. Green LEDs, when compared to blue LEDs, were shown to enter the high-injection regime at a lower voltage, which is attributed to their less favorable p-type transport characteristics. Green LEDs, with lower hole concentration and mobility, have a lower onset current density of the efficiency droop and a higher magnitude of the efficiency droop when compared to blue LEDs. The experimental results are in quantitative agreement with the imbalanced carrier transport causing the efficiency droop, thus providing guidance for alleviating the phenomenon of efficiency droop. Full article

(This article belongs to the Special Issue Solid State Lighting)

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17852 KiB

Open AccessArticle

The Effect of Solvents on the Performance of CH₃NH₃PbI₃ Perovskite Solar Cells

by Pao-Hsun Huang, Yeong-Her Wang, Jhong-Ciao Ke and Chien-Jung Huang

Energies 2017, 10(5), 599; https://doi.org/10.3390/en10050599 - 29 Apr 2017

Cited by 40 | Viewed by 7304

Abstract

The properties of perovskite solar cells (PSCs) fabricated using various solvents was studied. The devices had an indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)/CH₃NH₃PbI₃ (fabricated by using various solvents)/fullerene (C₆₀)/bathocuproine (BCP)/silver (Ag) structure. The solvents used were dimethylformamide (DMF), γ-butyrolactone (GBL), dimethyl sulfoxide (DMSO), a mixture of DMSO and DMF (1:1 v/v), and a mixture of DMSO and GBL (DMSO: GBL, 1:1 v/v), respectively. The power conversion efficiency (PCE) of the device fabricated using DMF is zero, which is attributed to the poor coverage of CH₃NH₃PbI₃ film on the substrate. In addition, the PCE of the device made using GBL is only 1.74% due to the low solubility of PbI₂ and CH₃NH₃I. In contrast, the PCE of the device fabricated using the solvents containing DMSO showed better performance. This is ascribed to the high solubilization properties and strong coordination of DMSO. As a result, a PCE of 9.77% was obtained using a mixed DMSO:GBL solvent due to the smooth surface, uniform film coverage on the substrate and the high crystallization of the perovskite structure. Finally, a mixed DMSO: DMF:GBL (5:2:3 v/v/v) solvent that combined the advantages of each solvent was used to fabricate a device, leading to a further improvement of the PCE of the resulting PSC to 10.84%. Full article

(This article belongs to the Special Issue Solid State Lighting)

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3257 KiB

Open AccessArticle

How Smart LEDs Lighting Benefit Color Temperature and Luminosity Transformation

by Yu-Sheng Huang, Wei-Cheng Luo, Hsiang-Chen Wang, Shih-Wei Feng, Chie-Tong Kuo and Chia-Mei Lu

Energies 2017, 10(4), 518; https://doi.org/10.3390/en10040518 - 11 Apr 2017

Cited by 19 | Viewed by 5029

Abstract

Luminosity and correlated color temperature (CCT) have gradually become two of the most important factors in the evaluation of the performance of light sources. However, although most color performance evaluation metrics are highly correlated with CCT, these metrics often do not account for light sources with different CCTs. This paper proposes the existence of a relationship between luminosity and CCT to remove the effects of CCT and to allow for a fairer judgment of light sources under the current color performance evaluation metrics. This paper utilizes the Hyper-Spectral Imaging (HSI) technique to recreate images of a standard color checker under different luminosities, CCT, and light sources. The images are then analyzed and transformed into interpolation figures and equal color difference curves. This paper utilizes statistic tools and symmetry properties to determine an exponential relationship between luminosity and CCT in red-green-blue (RGB) LED and OLED light sources. Such a relationship presents an option to remove the effects of CCT in color evaluation standards, as well as provide a guide line for adjusting visual experience solely by adjusting luminosity when creating a lighting system. Full article

(This article belongs to the Special Issue Solid State Lighting)

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7505 KiB

Open AccessArticle

Scale-Dependent Light Scattering Analysis of Textured Structures on LED Light Extraction Enhancement Using Hybrid Full-Wave Finite-Difference Time-Domain and Ray-Tracing Methods

by Tsung-Xian Lee and Ching-Chia Chou

Energies 2017, 10(4), 424; https://doi.org/10.3390/en10040424 - 23 Mar 2017

Cited by 10 | Viewed by 5709

Abstract

A multiscale model that enables quantitative understanding and prediction of the size effect on the scattering properties of micro- and nanostructures is crucial for the design of light-emitting diode (LED) surface textures optimized for high light extraction efficiency (LEE). In this paper, a hybrid process for combining full-wave finite-difference time-domain simulation and a ray-tracing technique based on a bidirectional scattering distribution function model is proposed. We apply this method to study the influence of different pattern sizes of a patterned sapphire substrate on GaN-based LED light extraction from the micro-scale to the nano-scale. The results show that near-wavelength–scale patterns with strong diffraction are not expected to enhance the LEE. By contrast, micro-scale patterns with optical diffusion behavior have the highest LEE at a specific aspect ratio, and subwavelength-scale patterns that have antireflection properties show a marked enhancement of the LEE for a wide range of aspect ratios. Full article

(This article belongs to the Special Issue Solid State Lighting)

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