Utilization of Trapped Optical Modes for White Perovskite Light-Emitting Diodes with Efficiency over 12%
Ziming ChenZhenchao LiZhen ChenRuoxi XiaGuangruixing ZouLinghao ChuShi‐Jian SuJunbiao PengHin‐Lap YipYong Cao
105
Citation
29
Reference
10
Related Paper
Citation Trend
Keywords:
White (mutation)
Light-emitting diodes (LEDs) degradation during 10 000 hours and the influence of ultrasonic action on the InGaN LEDs were investigated. The model of LED degradation is suggested and based on 1) common LED is the combination of parallel Small-LEDs (S-LED) which correspond to the areas with different concentration of In atoms; 2) redistribution of In atoms in quantum-dimensional active region of blue InGaN LED under strong piezoelectric effect and spontaneous polarization induced by ultrasonics; 3) the ultrasonics which is used in creating LEDs can make defects in heterostructures and they (during LEDs work) are heated by current or ultrasonic, can be increased and that's why nonradiation recombination decreases LEDs efficiency. It can be said that great current density flows through areas with low In concentration and therefore S-LEDs are "burned out" and irradiate less. At the areas with average In concentration the densities decrease. That is why electroluminescence spectrum, radiation power, luminous intensity characteristics are shifted to the long wave region. All that also exactly corresponds with our experimental results of LEDs degradation investigation during 10 000 hours.
Wide-bandgap semiconductor
Cite
Citations (2)
Multi-channel light-emitting diode (LED) light sources have been developed for various applications in lighting, but especially for spectrum-tunable lighting. However, how to select the optimal combination of LEDs for these light sources is rarely discussed. Unlike the negative-pruning process which operates by removing LEDs from a set of available LEDs based on an unrealizable negative-coefficient criterion alone, the proposed pruning process removes LEDs so as to minimize the synthesis error. This method not only produces the same optimal set of LEDs as those identified by the full-search method but also suggests when using phosphor-converted LEDs is beneficial. It does this by investigating the trade-off between the full width half maximum of the LEDs and the number of LEDs.
Pruning
Cite
Citations (20)
Light extraction in thin-film GaN light-emitting diodes (LEDs) prepared with Si substrates pretreated by surface roughening and imbedded electrodes were studied. The LEDs were fabricated with a roughened p-GaN layer, followed by epilayer transferring. There are four types of LEDs: conventional LEDs (C-LED), n-side-up thin GaN LEDs with imbedded electrodes and a KOH-roughened n-GaN (first-type LED), p-side-up thin GaN LEDs with a KOH-roughened n-GaN (second-type LED), and n-side-up thin GaN LEDs with imbedded electrodes and without KOH-roughened n-GaN (third-type LED). The electrical properties of the LEDs are almost the same. However, they differ in luminance intensity. The luminance intensities (at 350 mA) of C-LED, first-type, second-type, and third-type LEDs are 3468, 9105, 7610, and 7047 mcd, respectively. The brightest LED is first-type LED. This may be due to emission surface with pyramidal-textured surface and without light shading electrodes. They enhance the light extraction for first-type LEDs.
Wide-bandgap semiconductor
Cite
Citations (7)
국내 LEDs 산업의 발달함에 따라 LEDs 가격이 지속적으로 낮아지며 광량과 내구성이 좋은 LEDs가 개발되어 불량한 기후 조건에서 작물의 수량을 증진하기 위하여 시설재배 농가를 중심으로 원예작물에 LEDs 이용을 위한 시도가 이뤄지고 있다. 이에 본 실험은 적색과 초적색 LEDs 보광이 ``홍로``/M.26 사과의 과중분포 및 과실품질에 미치는 영향을 구명하여 사과에서 LEDs 보광이 과실의 품질향상에 도움이 될수 있는지를 구명하기 위하여 실험하였다. 실험 처리는 대조구인 무처리구, 적색광(660nm) 2, 4시간 조사구, 초적색광(730nm) 2, 4시간 조사구의 5처리를 난괴법 3반복으로 실험하였다. LEDs 보광은 일몰후 처리별로 조사하였으며 처리시기는 화아분화기와 착색기에 각각 1개월씩 보광하였다. 실험결과 적색광 LEDs 보광에 의해 대조구에 비해 적색 LED 처리구에서 엽중이 늘어났으나 초적색 LEDs 보광에서는 엽중이 감소하였으며 보광시간이 길어질수록 더욱 감소하였다. 2009년에는 무처리구인 대조구에 비해 LEDs 처리구에서 과중이 증가하였으며 특히 적색광 LEDs 처리구에서 188g 이하의 소과 발생도 없었고 300g 이상 과실도 많았다. 2010년에는 250g 이상 과실이 대조구에 비해 적색광 2, 4시간 보광에서 증가하였으나 초적색광 보광에서는 대조구에 비해 감소하였다. 과실의 경도는 대조구에 비해 초적색광 2, 4시간 보광에서 증가하였으며 당도에서는 큰 차이를 나타내지 않았다. 착색도에 있어서는 적색 LEDs 처리구가 대조구에 비해 Hunter a 값이 낮아지는 경향을 나타냈으나 초적색광에서는 높아지는 경향을 나타냈다. 이상의 결과를 통해 살펴보면, 적색광은 홍로 사과의 과중을 증가시켰으나 초적색광은 Hunter a 값을 높이는 결과를 나타냈다. 이에 앞으로 사과원에서의 LEDs의 효과적인 이용을 위해 적색광과 초적색광 단용처리가 아닌 혼합처리를 하여 각각의 광원의 효과가 상승적으로 작용하는지에 대한 추가적인 연구가 필요할 것으로 판단되었다.
Cite
Citations (0)
The light extraction process in GaN-based light emitting diodes (LEDs) is studied in this paper. In order to increase the light extraction efficiency of large area LEDs, several novel LED geometries are discussed. The light propagation in the LEDs is simulated numerically by using the finite-difference time-domain (FDTD) method. It is shown that the following improvements in the GaN-based LEDs are very effective for increasing the light extraction: (1) To fabricate GaN micro-pyramid array on the surface of the LED, which guides the generated light to the surface; (2) To make inverted V-shaped groove formation on the GaN layer, which restricts the average length of ray path in the LEDs and refracts the waveguide-mode light to the surface; (3) To separate the LED epilayer from its substrate and then mount it on a metal mirror base, which is used to reflect the backside light to the LED surface. The FDTD simulation results show clearly that these improved geometries guide most of the internal luminescence to escape from the LED, and increase greatly the external light-extraction efficiency of GaN-based LEDs.
Cite
Citations (11)
Interconnected microdisk light-emitting diodes (μ-LEDs) have been fabricated from InGaN/GaN single quantum wells grown by low pressure metal organic chemical vapor deposition. These interconnected μ-disk LEDs fit into the same device area taken up by a conventional broad-area LED. The performance characteristic of these interconnected μ-disk LEDs, including I–V and L–I characteristics as well as electroluminescence spectra have been measured and compared with those of the conventional broad-area LEDs. For interconnected μ-disk LEDs, while VF, the forward biased voltage at 20 mA, was slightly increased, the emission efficiency was increased by as much as 60% over the conventional LEDs for a fixed device area. The results thus suggested that replacing a conventional broad-area LED with an interconnected μ-disk LED, the external quantum efficiency can be significantly enhanced. Finally, the fabrication processes of the interconnected μ-disk LEDs are almost the same as those of the conventional broad-area LEDs. It is thus expected the total yield of these interconnected μ-disk LEDs to be the same as the conventional broad-area LEDs. The present method of utilizing interconnected μ-disk LEDs for improving the brightness of LEDs is applicable to other semiconductor LEDs as well as polymer and organic LEDs.
Quantum Efficiency
Wide-bandgap semiconductor
Cite
Citations (127)
During the past few years several manufacturers have introduced white Light Emitting Diodes (LEDs). At the present time these LEDs do not provide sufficient luminous flux for general lighting applications. Many manufacturers are studying the possibility of grouping several LEDs and overdriving them to produce more luminous flux. The impact of higher drive current on long-term performance of LEDs is not well known within the lighting community. Therefore, an experimental study was conducted to investigate the photometric characteristics of white LEDs as a function of time for different drive currents. The LEDs investigated in this study were the 5-millimeter type that uses GaN-based blue LEDs and Y3Al5O12 (yttrium aluminum garnet) phosphors (YAG phosphors). These LEDs produced 65 percent more light output at 55 mA compared to the light output at 20 mA. Groups of ten LEDs were driven continuously at constant current 20, 30, 50, 70, 90, and 110 mA and their relative light output were monitored at regular intervals for over 4000 hours. The light output degradation rate increased with increasing drive currents. Typically, LED manufacturers do not recommend driving these LEDs above 20 mA. However, it was noticed that the light output of these LEDs degraded to 65% of its initial value around 4000 hours even for those LEDs driven at 20 mA, which is the manufacturer recommended value for drive current. Considering the amount of flux produced by these 5 mm type white LEDs and their light output degradation rate, they are not yet suitable for general lighting applications.
Luminous flux
Luminous efficacy
Radiant flux
Cite
Citations (62)
In this letter, GaN-based high-voltage light-emitting diodes (HV-LEDs) arrays with 16 microchips connected in series are fabricated. The light output power-current-voltage (LOP-I-V) characteristic of HV-LEDs is measured. Under input power of 1.1 W, the LOP of HV-LEDs is enhanced by 11.9% compared to traditional high power light-emitting diodes (THP-LEDs) with the same chip size. Due to the reduced metal shadow effect and better current spread, the HV-LEDs exhibit higher light extraction efficiency under the same current density, which is simulated by a 3-D ray tracing method. As a result, the luminous efficiency of HV-LEDs is 21.6% higher than that of THP-LEDs under input power of 1.1 W. Furthermore, the efficiency droop of HV-LEDs is reduced to half of that of THP-LEDs.
Wide-bandgap semiconductor
Cite
Citations (17)
GaN-based light-emitting diodes (LEDs) with graded-thickness quantum wells and barriers (GMQW-LEDs) are fabricated and researched in this letter. The light power and carrier distribution of GMQW-LEDs are compared with those of LEDs with original uniform MQW (OR-LEDs), graded-thickness quantum wells (GQW-LEDs), and graded-thickness quantum barriers (GQB-LEDs) through numerical simulation, respectively. The experimental results show that light power of GMQW-LEDs is enhanced significantly compared with that of OR-LEDs. The simulation results reveal that GMQW-LEDs show light output power enhancements of 25.7%, 14.3%, and 9.2% compared with OR-LEDs, GQW-LEDs, and GQB-LEDs at current density of 100 A/cm 2 , respectively. This is due to the superior hole distribution in quantum wells, which inhibits the electron leakage and enhances the radiative recombination.
Quantum Efficiency
Wide-bandgap semiconductor
Cite
Citations (4)
The purpose of this study was to determine optimum condition for the cultivation of Chlorella sp. FC-21, which is a freshwater microalgae, using light emitting diodes (LEDs). Specific growth rate and cell concentration were measured for the reactors at the illumination of different wavelengths of LEDs. Among various types of LEDs, red LEDs were the most effective light source, and also greatest increases of specific growth rate and cell concentrations were obtained when light intensity of red LEDs increased. From this study, we found that red LEDs were the most appropriate light source for the cultivation of Chlorella sp. FC-21.
LED lamp
Light intensity
Cite
Citations (2)