Spectra Of Light-emitting Diodes Research Articles

Efficient Pure Blue Light-Emitting Diodes Based on CsPbBr3 Quantum-Confined Nanoplates

Exploitation of next-generation blue light-emitting diodes (LEDs) is the foundation of the revolution in lighting and display devices. Development of high-performance blue perovskite LEDs is still challenging. Herein, 4-aminobenzenesulfonic acid (SA) is introduced to passivate blue CsPbBr3 nanoplates (NPLs), reducing the ionic migration via a more stable Pb2+-SO3-- formation, and the trap state density of films shows a 50% reduction. The inevitable Br- vacancy defects after the multistep washing process can be suppressed by a suitable MABr treatment, which can boost the external quantum efficiency (EQE) performance. It should be noted that the coverage of NPL films is another key factor to realize reproducible pure blue electroluminescence (EL). Therefore, we proposed an alternate droplet/spin coating method to improve the coverage and thickness of NPL layer to prevent hole transport layer emission and increase the reproducibility of LED performance and spectra. Furthermore, we designed hole transport layers to decrease the hole transport barrier and improve the energy-level alignment. According to SA passivation, MABr treatment, alternate droplet/spin coating method, and device structure optimization, a CsPbBr3 NPL-based pure blue (0.138, 0.046) LED with 3.18% maximum EQE can be achieved, and the half-lifetime of EL can be enhanced 1.71 times as compared to that of the counterpart LED without SA. Both performance and stability of pure blue NPL LEDs can be greatly improved via ligand passivation, alternate droplet/spin coating method, and device structure optimization, which is a trend to promote the development of pure blue perovskite LEDs in future.

High intensity and red enriched LED lights increased the growth of lettuce and endive

Changes in plant responses have been associated with different fractions of the visible spectrum and light intensity. Advances in light-emitting diodes (LED) have enabled the study of the effect of narrow wavelengths on plant growth and antioxidant compound synthesis. LED technology also facilitates the incorporation of light sources in a controlled setting where light spectra and intensity can be regulated. The objective of this study was to compare the effect of two commercial light spectra (S1: standard white light with 32.8% blue, 42.5% green, 21.7% red, and 2.4% far-red; S2: AP67 spectrum, designed for horticultural growth, with 16.9% blue, 20.5% green, 49.7% red and 12.3% far red) at two light intensities [low intensity (78 μmol m–2s–1 of photons for S1 and 62 μmol m–2s–1 for S2, and high intensity (HI) (102 and 100 μmol m–2s–1 for S1 and S2, respectively)] on growth and antioxidant compound contents in two leafy vegetables: endive (Cichorium endivia L.) and lettuce (Lactuca sativa L.). Fresh weight (FW), dry weight (DW), and DW% of plants were taken as growth indicators. In addition, leaf number, soil plant analysis development index, leaf area (LA), and specific leaf area were also evaluated. Antioxidant synthesis was measured as total phenol content, total flavonoid content, and antioxidant activity. The results showed that S2 and HI increased the FW, DW, and LA in both species. On the other hand, antioxidant compound contents were significantly increased by HI but did not vary with the spectrum. Highlights - The spectra of LED affected leaf number in lettuce and endive. - S2 spectrum improved growth parameters of both leafy vegetables. - Light intensity improved growth parameters of both leafy vegetables. - Antioxidant compound contents were significantly increased by high intensity LED light.

Morphogenetic and physiological effects of LED spectra on the apical buds of Ficus carica var. Black Jack

The use of artificial light sources such as light-emitting diodes (LEDs) has become a prerequisite in tissue culture studies to obtain morphogenetic enhancements on in vitro plants. This technology is essential for developmental enhancements in the growing plant cultures due to its light quality and intensity greatly influencing the in vitro growing explants at a cellular level. The current study investigates the effects of different light-emitting diode (LED) spectra on the growth of apical buds of Ficus carica var. Black Jack. Ficus carica, commonly known as figs is rich in vitamins, minerals, and phytochemicals capable of treating microbial infections and gastric, inflammatory, and cardiac disorders. Apical buds of Ficus carica var. Black Jack, presented morphogenetic changes when grown under six different LED spectra. The highest multiple shoots (1.80 per growing explant) and healthy growing cultures were observed under the blue + red LED spectrum. Wound-induced callus formation was observed on apical buds grown under green LED spectrum and discolouration of the growing shoots were observed on the cultures grown under far-red LED spectrum. Multiple shoots obtained from the blue + red LED treatment were rooted using 8 µM indole-3-acetic acid (IAA), and the rooted plantlets were successfully acclimatised. Compared with the other monochromatic LEDs, blue + red proved to be significantly better for producing excellent plant morphogeny. It is apparent that blue and red LED is the most suitable spectra for the healthy development of plants. The findings have confirmed that the combination of blue + red LED can potentially be used for enhancing growth yields of medicinally and commercially important plants.

Effect of different wavelengths of LED light on the growth, chlorophyll, β-carotene content and proximate composition of Chlorella ellipsoidea

Chlorella ellipsoidea is a freshwater green microalga that has great prospect for the sustainable development of aquaculture industry. Microalgae require optimal lighting conditions for efficient photosynthesis. The key to cost-effective algal biomass production is to optimize algae growth conditions. This study aimed to investigate the effects of various wavelengths viz. white (380–750 nm), green (510 nm), blue (475 nm), and red (650 nm) light-emitting diodes (LEDs) on the growth, pigment content (chlorophyll-a, chlorophyll-b, and β-carotene), and proximate composition of C. ellipsoidea with a photoperiod of 12 h:12 h light: dark cycle under indoor environmental conditions. C. ellipsoidea was cultured in Bold's Basal Medium for 18 days. The cell density (125.36×105 cells ml−1), cell dry weight (58.9 ± 4.57 mg L−1), optical density (1.66 ± 0.08 g L−1), chlorophyll-a (7.31 ± 0.04 μg ml−1), chlorophyll-b (2.73 ± 0.13 μg ml−1), and β-carotene (0.39 ± 0.04 μg ml−1) content of C. ellipsoidea were significantly (P < 0.05) higher at 15th-day when cultured under blue LED light exposure. Significantly lower growth and nutritional values were obtained under red LED light exposure compared to the control and other LEDs spectra. In Pearson correlation analysis, the cell density and cell dry weight values showed a strong positive correlation with the values of pigment contents of C. ellipsoidea in all the treatments. The LEDs light spectra showed significant effects on proximate composition of C. ellipsoidea. Protein and lipid contents of C. ellipsoidea were significantly higher in blue LED growth conditions compared to white, green, and red LEDs. C. ellipsoidea cells were 3˗7.04 μm in size and the maximum area of the cell was 38.94 μm2 in blue LED treatment. Results of this study demonstrated that blue LED light spectra was the most suitable condition to induce nutritionally rich biomass production of C. ellipsoidea, which can be used as a potential source of fish feed towards sustainable aquaculture.

Enhancement of the near-band-edge electroluminescence from the active ZnO layer in the ZnO/GaN-based light emitting diodes using AlN-ZnO/ZnO/AlN-ZnO double heterojunction structure

In this work, an AlN-ZnO/ZnO/AlN-ZnO double heterojunction (DH) structure prepared using the cosputtering technology was deposited onto the p-type GaN epitaxial layer. The indiffusion of the oxygen atoms to the p-GaN epilayer was obstructed as the cosputtered AlN-ZnO film inset between n-ZnO/p-GaN interface. The near-ultraviolet (UV) emission from this ZnO/GaN-based light emitting diode (LED) was greatly improved as compared to an n-type ZnO film directly deposited onto the p-GaN epilayer. Meanwhile, the native defects in the n-ZnO layer associated with the green luminescence was less likely to form while it was sandwiched by the cosputtered AlN-ZnO film. As the thickness of the active n-ZnO layer in the DH structure reached 10 nm, the near-band-edge (NBE) emission became the predominated luminescence over the resulting LED spectrum.

Energy-Saving LED Light Affects the Efficiency of the Photosynthetic Apparatus and Carbohydrate Content in Gerbera jamesonii Bolus ex Hook. f. Axillary Shoots Multiplied In Vitro.

Simple SummaryGerbera is one of the most important ornamental plants on the cut flower market. The basic reproduction methods of numerous cultivars of this species are in vitro techniques. In in vitro cultures, all plant growth conditions are controlled, including the light (intensity, quality, and duration). In tissue cultures, light quality is the most important factor that influences plant morphogenesis (growth and development). Light emitting diodes (LEDs), in contrast to the commonly used fluorescent lamps, allow for adjusting the light quality to the specific requirements of plants. LEDs are also energy-efficient and contain no harmful substances (e.g., mercury). The aim of the study was to analyze the effect of different light qualities emitted by LEDs during in vitro multiplication of Gerbera on its metabolic and physiological development. We compared endogenous carbohydrate content in the tissues and the condition of the photosynthetic apparatus in plants grown under fluorescent lamps and LED light. The study showed that the use of LEDs did not disturb the secondary metabolism of carbohydrates and the multiplied shoots were of high quality. The mixture of red and blue LED light in a 7:3 proportion is recommended for gerbera micropropagation. This light quality positively influenced the functioning of the photosynthetic apparatus.An energy-saving light emitting diode (LED) system allows for adjustment of light quality, which affects plant development and metabolic processes in in vitro cultures. The study investigated the content of endogenous carbohydrates and the condition of the photosynthetic apparatus of Gerbera jamesonii Bolus ex Hook. f. Our aim was to analyze the effects of different LED light qualities—100% red light (R LED), 100% blue (B LED), a mixture of red and blue (7:3) (RB LED), and a fluorescent lamp as a control (Fl)—during the multiplication of axillary shoots. After 40 days, the culture measurements were performed using a non-invasive pulse amplitude modulation (PAM) fluorimeter. Sugar content was assessed with high performance liquid chromatography (HPLC). Two forms of free monosaccharides (glucose and fructose), two sugar alcohol derivatives (inositol and glycerol), and seven forms of free oligosaccharides were identified. Of those, glucose content was the highest. LEDs did not disturb the sugar metabolism in multiplied shoots. Their monosaccharides were three times more abundant than oligosaccharides; the same results were found in plants grown under control light. R light depleted the performance of the photosynthetic apparatus and caused its permanent damage. The RB LED spectrum ensured the most efficient non-photochemical quenching of the photosystem II (PS II) excitation state and high shoot quality.

The use of mixed light-emitting diodes and natural light in combination with daylength affects turkey hen performance, eye development, and feather coverage

Lighting is a complex management tool in turkey production, controlled by three parameters; daylength, intensity, and chromaticity. As light-emitting diodes (LED) increase in popularity as alternatives to traditional light sources, research regarding LED impacts on commercial-type turkey production is lacking. Therefore, turkey hens of the same strain were reared under experimental brooding and grow-out conditions with six lighting treatments. An environmentally and light controlled facility (ECF) consisted of 5,000 Kelvin (K) LED or 5,000K + far-red LED (639nm) (RED) with either 12h short or 18h long daylength to test LED spectra. In the remaining treatments, hens were exposed to sunlight in a curtain-sided facility (CSF) as two treatments 1) natural decreasing daylength from September to November (NAT) or 2) natural daylight + 5,000 K LED lighting with an 18h long blocked daylength (BLK). The intensity was 9 footcandles in the ECF and naturally fluctuating in the CSF. Hen's performance was evaluated at 5, 9, and 14 weeks for eye development and feather coverage. Hens brooded and grown-out under NAT light had significantly increased body weight gain compared to BLK hens for the same period. Hens reared with RED LED spectrum had significantly increased eye anterior-posterior distance than birds raised in the NAT treatment. A significant reduction in red heat signature on the breast tissue in the NAT treatment compared to all other 18h treatments indicated improved feather coverage. However, these same results were not observed during serum thyroid hormone analysis. While turkey hens reared under different lighting programs had similar ending performance, lighting parameters significantly affected bird performance during the growing period, bird's eye development, and body feather coverage. Therefore, potential effects on growth patterns and physiology should be considered when choosing a LED lighting program for turkeys

Soilless System with Supplementary LED Light to Obtain a High-Quality Out-of-Season Production of Green Beans

Green bean (Phaseolus vulgaris L.) is one of the most important sources of vegetable proteins in the world and it is cultivated all year round, but the light availability, during the dark season, limited its growth. Nevertheless, recent studies conducted on greenhouse horticulture demonstrated that, with the application of light emitting diodes (LEDs) as supplementary light (SL) technology, it is possible to overcome this limitation. Consequently, during the experiment conducted, two cultivars of green bean (‘Saporro’ and ‘Maestrale’) were grown with a soilless system in a cold greenhouse during the fall-winter period. To increase the photoperiod and the daily light integral (DLI), early in the morning, four hours of red (R), blue (B) and red+blue (R + B) supplementary light were supplied by LEDs at 180 μmol·m−2·s−1 (PPFD) at plants level. Plants grown under LEDs improved the yield and the gas exchange system compared with the plants grown under natural light; when B light was supplied as a sole source of SL, it increased the dry matter content and the brightness (L*) of the pods. Between the cultivars, ‘Maestrale’ produced 20 g∙plant−1 of pods more than ‘Saporro’ but the latter’s colour was brighter (L*) and greener (a*), and ‘Saporro’ also showed the highest photosynthetic efficiency (ΦPSII). In conclusion, ‘Maestrale’ and ‘Saporro’ obtained encouraging out-of-season yields under different LED spectra, but among those B light seems to improve overall crop performances and pods quality.

Investigation of a Separated Short-Wavelength Peak in InGaN Red Light-Emitting Diodes

We fabricated indium gallium nitride (InGaN) red light-emitting diodes (LEDs) with a peak emission wavelength of 649 nm and investigated their electroluminescence (EL) properties. An additional separated peak in the EL spectrum of the red LEDs at 20 mA was observed at 465 nm. This additional peak also exhibits a blue-shift with increasing currents as does the main emission peak. Using high-resolution microscopy, we observed many point-like emission spots in the EL emission images at the currents below 1 mA. However, these emission spots cannot be identified at currents above 5 mA because the red emission from quantum wells (QWs) is much stronger than that emitted by these spots. Finally, we demonstrate that these emission spots are related to the defects generated in red QWs. The measured In content was lower at the vicinity of the defects, which was regarded as the reason for separated short-wavelength emission in red InGaN LEDs.

Comparing and Quantifying Indoor Performance of Organic Solar Cells

AbstractWith increasing efficiencies of non‐fullerene acceptor‐based organic solar cells, thin‐film technology is becoming a promising candidate for indoor light harvesting applications. However, the lack of standardized comparison methods makes it difficult to quantify progress and to compare indoor performance. Herein, a simple method to calculate the efficiency of solar cells under any possible light source and illuminance with only using simple standard measurements (current–voltage curves and quantum efficiency) is presented. Thereby, equal evaluation conditions are ensured, so that indoor solar cells can be ranked and compared according to their efficiency. Efficiencies are shown to typically vary by ±20% when using different different light emitting diode spectra with color temperatures ranging from 2700 to 6500 K. Calculations based on a detailed balance model indicate that the optimal bandgap of the absorber material depends on the used light source and ranges between 1.75 and 2 eV. The approach is validated by comparison with literature data and many calculated efficiencies match well with experimental data obtained with a specific light source. However, some reported efficiencies cannot be reproduced with the model, which highlights the need to reassess low light measuring techniques. Furthermore, a script is provided for use by the community.

Effect of LED Spectrum on the Quality and Nitrogen Metabolism of Lettuce Under Recycled Hydroponics.

Light quality optimization is an efficient method for improving the growth and quality of lettuce in plant factories. In this study, lettuce seedlings were illuminated under different light-emitting diode (LED) lights, namely, red-blue (RB), red-blue-green (RBG), red-blue-purple (RBP), and red-blue-far-red (RBF) LED lights, to investigate the effect of light quality on growth, quality, and nitrogen metabolism. The combination of 75% red and 25% blue light was set as the basic light source, and 20% of green, purple and far-red light were added to basic light source, respectively. All the treatments were set to 200 μmol m–2 s–1. Results showed that the fresh weight and dry weight of aboveground lettuce under RBG, RBP, and RBF treatments were significantly lower than those under the RB treatment because of the decrease in the effective photon flux density for chlorophyll absorption. The vitamin C content of the lettuce leaves was increased by about 23% with the addition of purple light. For nitrate reduction, the addition of green light significantly increased the nitrite content of the lettuce leaves. It also promoted the reduction from nitrite to ammonium through the activation of the nitrite reductase (NiR) expression and enzyme activity. The nitrate and ammonium content decreased with the addition of purple light because of the inhibited NR and NiR expression and enzyme activity. For nitrogen assimilation, individual (e.g., Asp, Glu, and Leu) and total amino acids were induced to increase by adding green, purple, and far-red light. The addition of light was hypothesized to have inhibited protein biosynthesis, thereby causing the accumulation of amino acids. Correlation analysis showed that the relative expression levels between HY5 and NR/NiR presented a significantly negative correlation. Transcription factor HY5 might mediate the regulation of light quality on nitrogen metabolism by inhibiting NR and NiR expressions. It might also exert a negative effect on nitrate reduction. Further studies via genome editing techniques on the identification of HY5 functions for nitrate assimilation will be valuable. Nevertheless, the results of this work enrich the understanding of the effect of light quality on nitrate metabolism at the level of gene expression and enzyme activity.

The correlation between limiting efficiency of indoor photovoltaics and spectral characteristics of multi-color white LED sources

The correlation between the optimal performance of indoor photovoltaics (IPVs) and spectral characteristics of white light-emitting diode (LED) sources has been investigated theoretically. We calculated the Schockley–Queisser limit of IPVs under multi-color white LEDs with different correlated color temperature (CCT), color rendering index (CRI) and luminous efficacy of radiation (LER). It is found that the optimal bandgap for an IPV cell is not only influenced by CCT, but also by LER and CRI. However, the main factor that affects the maximum power conversion efficiency (PCE) is CCT, and the maximum PCE is relatively independent of the CRI and LER under the same condition of CCT. The maximum PCE decreases with the increase of CCT. Based on the analysis of the energy loss within IPVs, it is found that the value of the optimal bandgap is sensitive to the fraction of red light in the spectrum of white LEDs. The maximum PCE is primarily limited by the relaxation to band edge loss, which is caused by the high-energy blue or cyan light in the spectrum of white LEDs.

Research on high luminous efficiency, high color rendering index chips on board light emitting diode and excitation and excitation saturation effect of phosphor

AbstractA kind of chips on board (COB) package of light emitting diode (LED) light source is designed and produced. By reducing the current density and using the mirror aluminum substrate with high reflectivity to improve the luminous efficiency. Meanwhile, three kinds of red phosphors with peak wavelength of 630 nm, 631 nm and 639 nm are added on the basis of yellow‐green phosphors, which increase within the range of red light LED spectrum composition, improve the LED color rendering index. The measurement results show that under 500 mA forward current, the luminous flux density of LED on the luminous surface with an area of 227 mm2 reaches 14.4 lm/mm2, the luminous efficiency reaches 175.5 lm/W, and the color rendering index reaches 89.3. It is found in the process of measuring the LED color temperature changes slightly with the current change, and by calculating that the proportion of blue photons in the LED spectrum is increasing gradually, the cause of this phenomenon is the phosphor excitation efficiency is saturation when the optical power density is high, which is influenced in two aspects: the proportion of photons absorbed by phosphor or the phosphor excitation efficiency decreases, the two factors together or separately cause the phosphor excitation saturation effect.

Light quality and quantity affect graft union formation of tomato plants

It is already known that there are many factors responsible for the successful formation of a graft union. However, the role of light has been little studied. In an anatomical study, Scanning Electronic Microscope (SEM) was used to explore the effects of different light-emitting diodes (LEDs) on graft union formation in grafted tomato. In addition, the expression genes related to Auxin hormone signaling pathway (SAUR67, AUX1, ARF30, and LAX3) was investigated. The obtained results showed that the concrescence process occurred faster under R7:B3 light conditions, as compared to blue (B) and white fluorescent (WFL) lights. Red light application caused a delay in the vascular tissue differentiation, which may lead to callus development on both sides, causing junctional failure and resulting in ineffective graft junctional arrangement. The expression of genes related to Auxin hormone significantly increased by R7:B3 application. We suggest that LED spectra affects the graft development of tomato plants and can improve the performance of grafted tomato seedlings.

Effects of light spectrum on morpho-physiological traits of grafted tomato seedlings.

It is already known that there are many factors responsible for the successful grafting process in plants, including light intensity. However, the influence of the spectrum of light-emitting diodes (LEDs) on this process has almost never been tested. During the pre-grafting process tomato seedlings grew for 30 days under 100 μmol m-2 s-1 of mixed LEDs (red 70%+ blue 30%). During the post-grafting period, seedlings grew for 20 days under the same light intensity but the lightening source was either red LED, mixed LEDs (red 70% + blue 30%), blue LED or white fluorescent lamps. This was done to determine which light source(s) could better improve seedling quality and increase grafting success. Our results showed that application of red and blue light mixture (R7:B3) caused significant increase in total leaf area, dry weight (total, shoot and root), total chlorophyll/carotenoid ratio, soluble protein and sugar content. Moreover, this light treatment maintained better photosynthetic performance i.e. more effective quantum yield of PSII photochemistry Y(II), better photochemical quenching (qP), and higher electron transport rate (ETR). This can be partially explained by the observed upregulation of gene expression levels of PsaA and PsbA and the parallel protein expression levels. This in turn could lead to better functioning of the photosynthetic apparatus of tomato seedlings and then to faster production of photoassimilate ready to be translocated to various tissues and organs, including those most in need, i.e., involved in the formation of the graft union.

Exponential fertilization on red-seed tree (Ormosia hosiei) seedlings subjected to contrasting light conditions: Do we really need intensive nutrient loading?

Exponential fertilization (EF) can feed seedlings with more nutrients than needed for growth and continuous lighting is expected to reduce the risk of loading at high application rate. In this study, red-seed tree (Ormosia hosiei Hemsley &amp; E. H. Wilson) seedlings were raised by EF at a low rate of 160 mg nitrogen (N) plant-1 (conventional) (N-phosphorus [P]-potassium [K], 12-9-12) and a high rate of 600 mg N plant-1 (intensive), which was adapted from previous studies with large-pot-seedlings. Both fertilizer regimes were nested to either of two light spectra from high-pressure sodium (HPS) and light-emitting diode (LED) sources with three replicates for each combined treatment. Seedlings subjected to the conventional regime in the LED spectrum showed better growth and greater biomass accumulation with higher leaf N and P contents than other ones. In the conventional fertilizer regime, the LED spectrum also resulted in higher photosynthesis shown by more pigments and higher N synthesis than the HPS spectrum. The HPS spectrum strengthened P synthesis in the intensive regime. The antioxidative activity was stimulated by a high dose of EF, hence excessive toxicity was likely induced. We recommend using the normal rate of 160 mg N plant-1 for the culture of red-seed tree seedlings with LED lighting to promote seedling quality without causing excessive nutrient toxicity.

An Approach for Designing Mixed Light-Emitting Diodes to Match Greenhouse Plant Absorption Spectra

We report a methodological approach for simulating luminary output radiation, which is achieved by mixing light-emitting diodes (LEDs) in order to match any plant absorption spectrum. Various recorded narrow-band LED spectra of different colors were first characterized and then fitted with a multi-Gaussian model. An optimizing procedure computed the optimal weighting of the relevant parameters so as to minimize the discrepancy between the combined spectrum and the reference target curve. The particle swarm optimization (PSO) method was applied because it is the most suitable technique for mono-objective situations. Within the useful spectral interval, the worst relative standard deviation between the optimized curve and recorded LED spectral power distribution (SPD) was 3.4%. When combining different LED types, the simulated light output showed that we could limit ourselves to selecting only five colored sources. This work will help us to design an optimized 200 W laboratory luminaire with a pulse-width switched-mode power supply.

Doping effect numerical comparison of band gap energy and active region range for GaN and GaAs based semiconductor

This work reports the effect of doping concentration on the energy-band structure of semiconductor materials. The research focuses on the resultant values of bandgap energy and its depletion region (length/area), based on the initial concentrations of doping which are the donors and acceptors. The energy-band diagram is simulated by initializing the various materials’ properties of Gallium Nitride (GaN) and Gallium Arsenide (GaAs), and solving the Poisson’s equation derived from Maxwell’s equation. The equation is solved by applying the finite difference method (FDM) and using the Newton-Raphson method. Both of these materials are compared with different doping concentrations (1×1013cm−3-1×1017cm−3). Taking the GaAs properties as the controlled variable, the band structure is validated with literature findings. The measured band gap energy of GaN changes from 1.5215eV to 7.6689eV, and GaAs, from 1.1330eV to 5.6431eV. It increases with the proportion to the doping concentration increments. However, when obtaining both of the spatial active regions for GaN and GaAs, it reduce from (1.9990μm-0.0790μm)x1μm2 and from (1.9990μm-0.0890μm)x1μm2 respectively. The findings show the effect of doping concentration on the semiconductor energy-band structure. Thus, the numerical system is expected to be used as the determination of the internal quantum efficiency, and the output spectrum of light-emitting diode (LED) chip.

Role of bulk- and interface-defects in spectrum-dependent energy harvesting of CZTSSe-based indoor photovoltaic devices

In this work, we theoretically investigate spectrum dependent energy harvesting of a thin-film indoor photovoltaic (PV) device, taking into account the role of defects. By numerically solving Poisson’s equation and the continuity equation under optical generation-recombination conditions, performance characteristics of a Cu2ZnSn(S,Se)4-based thin-film PV device have been evaluated under spectrally varying white light emitting diodes (LEDs). Without any loss of generality, the results of the experimentally validated theoretical model suggest that a thin-film PV device becomes significantly tolerant to both bulk and interface defects when a fraction of blue emission in the white LED spectra remains relatively low. For a white LED having cool white emission characteristics, the efficiency of a CZTSSe-based PV device can equal the efficiency of the CZTSSe solar cell, the experimentally reported champion, while having about two orders of magnitude higher interface defect density, as well as about twenty times higher bulk defect density. In addition, for all practical densities of both types of defects, the efficiency of the indoor PV device remains at least 20% higher than the efficiency obtained under AM1.5 solar irradiation. The underlying reasons behind such observations have been traced back to the wavelength dependent carrier generation recombination dynamics of the thin-film device stack. The results of this work in effect provide guidelines for designing low-cost yet energy-efficient indoor photovoltaic devices with defect-rich thin film material systems.

Effects of Light Intensity, Spectral Composition, and Paclobutrazol on the Morphology, Physiology, and Growth of Petunia, Geranium, Pansy, and Dianthus Ornamental Transplants

Under light-limiting conditions, many ornamental greenhouse-grown plants show undesired morphological characteristics, such as plant elongation (hypocotyl and epicotyl length) and low dry mass, which reduce plant quality. Research has shown that use of plant growth regulators (PGRs) and changes in both light intensity and spectral composition can reduce these undesired characteristics. However, little is known about the role of the combined effects of supplemental lighting and PGRs on the production of ornamental seedlings. The objective of this study was to characterize the combined and independent effects of light intensity, spectral composition, and PGR applications on the greenhouse production of ornamental transplants. Petunia (Petunia × hybrida), geranium (Pelargonium × hortorum), pansy (Viola × wittrockiana) and dianthus (Dianthus chinensis) were grown for 32–42 days under three supplemental light (SL) treatments: 1) high-pressure sodium (HPS), 2) light-emitting diodes (LEDs) with a 6 blue (B):5 green (G):89 red (R) (percent photon flux ratio), and 3) LEDs with 19B:81R (100 μmol m−2 s−1, 18 h photoperiod for all treatments). A control (No SL) was also included. In addition, a portion of plants were also sprayed with the paclobutrazol PGR (PBZ and No PBZ). The synergistic effects of the combination of PBZ and supplemental lighting resulted in the most compact plants, caused by a reduction in plant height by PBZ and an increase in dry mass by SL. However, PBZ reduced shoot dry mass of most plant species and light combinations. Plant compactness was greater under the 6B:5G:89R LED composition for petunia and when combined with PBZ for geranium than for plants under HPS lighting. Root dry mass of petunia, geranium, and pansy plants increased in response to SL compared with no SL by 2.4–5.7-fold. Results from the two LED spectra were unexpected; plants under 6B:5G:89R were more compact (petunia, geranium), had higher anthocyanin concentrations (petunia), were shorter (petunia, pansy, dianthus) and had less leaf area (petunia, pansy, dianthus) than plants in the SL treatment with a higher B and lower G PF (19B:81R). Supplemental lighting and PBZ can be used in conjunction or independently to improve plant morphology. The increased light from SL provided the most benefits by improving dry mass, compactness, and leaf number for most plant species. However, when PBZ was used in combination with SL, plant compactness increased for some species. The spectral composition of SL had an impact on plant growth and morphology, warranting additional research on plant responses to small changes in the spectral composition of SL.