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Performance Evaluation of Single-Junction Indoor Photovoltaic Devices for Different Absorber Bandgaps Under Spectrally Varying White Light-Emitting Diodes
摘要： In this article, we present a detailed theoretical study to predict performance characteristics of single-junction indoor photovoltaic (PV) devices operated under white light emitting diodes (LEDs) having different spectral characteristics. Efficiency limits of both ideal and practical PV converters have been evaluated considering illumination by commercially available white LEDs. The obtained results have been generalized for white LED sources having a wide range of correlated color temperatures (CCTs) and fraction of blue in their corresponding spectrum. Depending on bandgap of the absorber material, both positive and negative correlations are observed between photon conversion efficiency of PV devices and CCT values of the white LED sources. For material bandgaps of ～1.5 eV or lower, higher photon conversion efficiencies are obtained for warm glow white LEDs. On the contrary, white LEDs characterized to emit cool light are found to be more conducive for PV devices having absorber layer bandgaps of ～2 eV or higher. The observed characteristics have been explained in terms of linewidth of the main emission peak and relative intensity of blue emission peak of the irradiating white LED spectrum. Based on the analysis of photon yield, three distinct bandgap ranges of the PV absorber material have also been identified, each of which represents different dependence of PV device performances on the white LED spectral characteristics. These results in effect provide the necessary guidelines for designing homojunction, heterojunction, or tandem PV devices suitable for operation under different practical white LED sources.
关键词： red-green-blue (RGB) white light emitting diodes (LEDs),energy conversion efficiency,photon yield,Correlated color temperature,indoor photovoltaic (PV)
更新于2025-09-12 10:27:22
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Bandgap trimming and optical properties of Si <sub/>3</sub> N <sub/>4</sub> :Al microbelt phosphors for warm white light-emitting diodes
摘要： Si3N4:Al microbelts with tunable bandgap energy and resultant yellow-orange phosphors are prepared through a facile direct nitridation method. The bandgap energy of Si3N4:Al microbelts has been gradually trimmed from 2.58 eV to 2.67, 2.74 and 2.85 eV by regulating the Si/Al molar ratio from 1000 : 1 to 50 : 1. Si3N4:Al:Eu phosphors display a wide emission ranging from 500 to 800 nm when excited by a 450 nm blue LED light source. The crystal structure of Si3N4:Al microbelts is of the α-Si3N4 phase as characterized by X-ray diffraction, high-resolution TEM and crystal models. Si3N4:Al microbelts grow along the (012) stacking direction in a low doping concentration case and grow along the (011) stacking direction in a high doping concentration case. Theoretical calculation results show that Al prefers to occupy the low energy interstitial sites in the (012) plane. There are more substitutional sites in the (011) plane occupied by Al in the high doping concentration case with increasing the bandgap energy of Si3N4:Al. Warm white light emission has been achieved by precoating Si3N4:Al:Eu phosphors onto a blue LED chip, whose correlated color temperature (CCT) can be tailored from 3000 K to 6500 K by altering the phosphor amount, indicating a promising potential application of Si3N4:Al:Eu phosphors in warm white LEDs.
关键词： direct nitridation method,Si3N4:Al microbelts,tunable bandgap energy,yellow-orange phosphors,warm white LEDs
更新于2025-09-12 10:27:22
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An Efficient Method for LED Light Sources Characterization
摘要： Digital LED drivers capable of blending the spectrum of two LED ?xtures with different Correlated Color Temperatures through the LEDs’ power supply control are widespread. However, the digital control of lighting systems is possible only after a careful study of the LED’s response, in terms of illuminance and Correlated Color Temperature. The proposed work takes advantage of the Tunable White technology for the realization of an ef?cient method for LED light source characterization. In order to evaluate how the light changes as a function of the electric power supplied by the LED drivers, an experimental setup to characterize LED light sources has been designed. Starting from the data acquired from the experimental setup, a model for dimming the LED driver and obtaining the desired values of quality of light has been developed. The proposed model is based on the least squares method and its accuracy is evaluated by comparing the obtained values of illuminance and Correlated Color Temperature with those measured by an illuminance spectrophotometer. Results achieved an error of 0.3% for Correlated Color Temperature and 1.5% for illuminance using the proposed approximation functions.
关键词： smart lighting,LED light,tunable white technology,digital LEDs control,source characterization
更新于2025-09-12 10:27:22
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High perovskite-to-manganese energy transfer efficiency in single-component white-emitting Mn-doped halide perovskite quantum dots
摘要： Taking advantages of negligible reabsorption and no phase separation, single-component white-emitting phosphors are believed as new promising color conversion materials for white light-emitting diodes. As a potential candidate, Mn-doped lead halide perovskites are studied intensively, but rare works can realize pure white emission with a single component due to the challenge for realizing sufficient energy transfer efficiency from perovskite to Mn at the desirable emission wavelengths. In this work, we reported the synthesis of single-component white light halide perovskite quantum dots (QDs) by doping Mn into the host of CsPb(Cl/Br)3@CsPb(Cl/Br)x core–amorphous shell (CAS). The small size of zero-dimensional core in CAS structure has a strong quantum confinement effect, which can enhance the energy transfer efficiency from halide perovskite to Mn impurity dramatically. Our result shows 19.3 times higher energy transfer efficiency for Mn-doped CAS than that of ordinary Mn-doped CsPb(Cl/Br)3 nanocubes. As a result, as-prepared Mn-doped CAS QDs give rise to a white light emission with Commission Internationale de l’Eclairage (CIE) color coordinates of (0.37, 0.33). After blending with polystyrene (PS), Mn-doped CAS QDs can be used as a single-component color conversion material for assembling white light LEDs.
关键词： energy transfer efficiency,white-emitting phosphors,white light LEDs,Mn-doped lead halide perovskites,quantum dots
更新于2025-09-12 10:27:22
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Evidence of trap-assisted Auger recombination in low radiative efficiency MBE-grown III-nitride LEDs
摘要： By studying low radiative e?ciency blue III-nitride light emitting diodes (LEDs), we ?nd that the ABC model of recombination commonly used for understanding e?ciency behavior in LEDs is insu?cient and that additional e?ects should be taken into account. We propose a modi?cation to the standard recombination model by incorporating a bimolecular nonradiative term. The modi?ed model is shown to be in much better agreement with the radiative e?ciency data and to be more consistent than the conventional model with very short carrier lifetimes measured by time-resolved photoluminescence in similar, low radiative e?ciency material. We present experimental evidence that a hot carrier-generating process is occurring within these devices, in the form of measurements of forward photocurrent under forward bias. The forward photocurrent, due to hot carrier generation in the active region, is present despite the lack of any “e?ciency droop”—the usual signature of band-to-band Auger recombination in high-quality III-nitride LEDs. Hot carrier generation in the absence of band-to-band Auger recombination implies that some other source of hot carriers exists within these low radiative e?ciency devices, such as trap-assisted Auger recombination.
关键词： hot carrier generation,III-nitride LEDs,ABC model,trap-assisted Auger recombination,radiative efficiency
更新于2025-09-12 10:27:22
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The LED Paradox: How Light Pollution Challenges Experts to Reconsider Sustainable Lighting
摘要： In the 21st century, the notion of “sustainable lighting” is closely associated with LED technology. In the past ten years, municipalities and private light users worldwide have installed light-emitting diodes in urban spaces and public streets to save energy. Yet an increasing body of interdisciplinary research suggests that supposedly sustainable LED installations are in fact unsustainable, because they increase light pollution. Paradoxically, blue-rich cool-white LED lighting, which is the most energy-efficient, also appears to be the most ecologically unfriendly. Biologists, physicians and ecologists warn that blue-rich LED light disturbs the circadian day-and-night rhythm of living organisms, including humans, with potential negative health effects on individual species and whole ecosystems. Can the paradox be solved? This paper explores this question based on our transdisciplinary research project Light Pollution—A Global Discussion. It reveals how light pollution experts and lighting professionals see the challenges and potential of LED lighting from their different viewpoints. This expert feedback shows that “sustainable LED lighting” goes far beyond energy efficiency as it raises complex design issues that imply stakeholder negotiation. It also suggests that the LED paradox may be solved in context, but hardly in principle.
关键词： innovation,light pollution,light-emitting diodes (LEDs),artificial light at night (ALAN),sustainable lighting,outdoor lighting
更新于2025-09-12 10:27:22
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[IEEE 2019 15th International Conference on Telecommunications (ConTEL) - Graz, Austria (2019.7.3-2019.7.5)] 2019 15th International Conference on Telecommunications (ConTEL) - A Flexible OLED based VLC Link with m-CAP Modulation
摘要： In recent years there has been a growing interest in using organic light emitting diodes (OLEDs) for illumination in indoor environments. They offer attractive features such as flexibility and large active areas at a low cost; they are energy efficient and have higher illumination levels compared to silicone based LEDs. In addition, the utilization of OLEDs have increased in devices such as smart mobile phones and TVs because of their low thickness. This paper investigates the performance of an OLED based visible light communications (OVLC) system, using a curved and flat OLED with multiband carrierless amplitude and phase (m-CAP) modulation for m = 2 at different angles of incidence on the optical receiver. It is shown that the BER performance is improved (i.e., below the forward error correction (FEC) limit of 3.8×10-3) with the curved OLED when the optical receiver moving along a circular path for the viewing angles greater 40o compared to the flat OLED, which is advantageous in device to device communications.
关键词： m-CAP modulation,flexible organic LEDs,visible light communications
更新于2025-09-12 10:27:22
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[IEEE 2019 3rd International Conference on Circuits, System and Simulation (ICCSS) - Nanjing, China (2019.6.13-2019.6.15)] 2019 3rd International Conference on Circuits, System and Simulation (ICCSS) - Long-Term Effect of Visual Fatigue Caused by LEDs with Modulated Light
摘要： The visual fatigue caused by long-term work under steady light generated by fluorescent luminaires and fluctuated light generated by LED luminaires with different modulation depth was investigated through subjective reports of symptoms and physiological signals. Both the subjective feelings and the physiological results show that visual fatigue becomes more serious with increasing time under all the test lighting conditions. Compared to fluorescent luminaires, the LED luminaires with full-modulated light produced significantly severer symptoms. However, the LEDs with 75% modulation depth was fully accepted.
关键词： physiological signal,LEDs,visual fatigue,modulation depth,subjective symptom
更新于2025-09-12 10:27:22
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10.2: <i>Invited Paper:</i> Quantum Dots as a new generation of emitting materials in OLEDs
摘要： Colloidal quantum dots (QDs)-based light-emitting diodes (QD-LEDs) has been actively researched due to the potential impacts to the display and lighting industry base on the unique properties of QDs itself such as size-dependent bandgap tuneability, narrow emission spectrum, and low-cost solution-based processing. However, the most of promising results in the past used cadmium (Cd) contained II-VI semiconductor nanocrystals. Therefore, a considerable future task is to substitute Cd-containing QDs with less toxic materials. InP-based QDs is a promising material among the III-V semiconductor nanocrystals and it has been already applied in conventional and inverted QD-LED structure.
关键词： QD-LEDs,conventional QD-LEDs,quantum dot,InP/ZnSe/ZnS,InP,inverted QD-LEDs
更新于2025-09-11 14:15:04
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Fabricating GaN-based LEDs on (?2 0 1) <i>β</i> -Ga <sub/>2</sub> O <sub/>3</sub> substrate via non-continuous/continuous growth between low-temperature undoped-GaN and high-temperature undoped-GaN in atmospheric pressure metal-organic chemical vapor deposition
摘要： This study demonstrates two approaches to the growth of GaN-based LEDs on (?2 0 1)-oriented β-Ga2O3 single crystal substrates using metal-organic CVD under atmospheric pressure. One approach induces non-continuous growth between low-temperature undoped-GaN (u-GaN) and high-temperature u-GaN, whereas the other approach induces continuous growth. We observed the following reduction in the FWHM of X-ray diffraction rocking curves: GaN (0 0 2) on (?2 0 1) β-Ga2O3 substrate (from 464 to 342 arcsec) and GaN (1 0 2) (from 886 to 493 arcsec). An LED with six pairs of InGaN/GaN multiple quantum wells was successfully fabricated on the (?2 0 1) β-Ga2O3 single crystal substrate.
关键词： metal-organic chemical vapor deposition,X-ray diffraction,β-Ga2O3 substrate,non-continuous/continuous growth,GaN-based LEDs
更新于2025-09-11 14:15:04