High Intensity Illumination Research Articles

Kinetics of the permanent deactivation of the boron-oxygen complex in crystalline silicon as a function of illumination intensity

Based on contactless carrier lifetime measurements performed on p-type boron-doped Czochralski-grown silicon (Cz-Si) wafers, we examine the rate constant Rde of the permanent deactivation process of the boron-oxygen-related defect center as a function of the illumination intensity I at 170°C. While at low illumination intensities, a linear increase of Rde on I is measured, at high illumination intensities, Rde seems to saturate. We are able to explain the saturation by assuming that Rde increases proportionally with the excess carrier concentration Δn and take the fact into account that at sufficiently high illumination intensities, the carrier lifetime decreases with increasing Δn and hence the slope of Δn(I) decreases, leading to an apparent saturation. Importantly, on low-lifetime Cz-Si samples no saturation of the deactivation rate constant is observed for the same illumination intensities, proving that the deactivation is stimulated by the presence of excess electrons and not directly by the photons.

Single-Molecule FRET Probes a Transient Complex that Facilitates Binding of an Intrinsically-Disordered Protein

Intrinsically-disordered proteins (IDPs) are unfolded at the native condition and fold only when attaching to their binding partners. Even though IDPs often undergo large conformational changes, which may slow the binding process, the binding kinetics are sometimes surprisingly fast, close to those of diffusion-controlled reactions. IDPs usually contain a large number of charged residues and theory predicts that the association can be facilitated by the formation of a transient complex (TC) stabilized by the electrostatic attraction between an IDP and its binding target. Although the modulation of the association rate by ionic strength of the solution has been observed for a number of IDPs, TC has not been directly probed during the course of binding. To experimentally investigate the role of TC in fast binding, we employed single-molecule Forster resonance energy transfer (FRET) spectroscopy that monitors the conformational evolution of an IDP from the unbound state to the bound complex. We studied binding of the transactivation domain (TAD) of the tumor suppressor protein p53 (negatively charged, −10) and the nuclear co-activator binding domain (NCBD) of CBP (positively charged, +6). The N- and C-termini of TAD were labeled with Alexa 647 and Alexa 488 site-specifically and molecules were immobilized on a glass surface using a biotin-neutravidin linkage to monitor binding to unlabeled NCBD in solution. Because of the fast binding kinetics, the bound state, TC, and unbound state could not be clearly resolved in binned trajectories. Instead of binning, we used the maximum likelihood method (Gopich and Szabo, JPCB(2009)) to analyze photon trajectories collected at high illumination intensity and to measure the binding kinetics (photon count rate of 50 - 100 ms−1) and the lifetime of TC (photon count rate of 500 - 1000 ms−1). We found that the association rate reaches ∼ 1 x 109 M−1s−1, which is close to the diffusion-limited rate, and the lifetime of TC is relatively long (∼100 microsecond) compared to the kinetics at low ionic strength (∼ 0.04 M). More importantly, both quantities decrease significantly with the increasing ionic strength, indicating that the destabilization of TC results in the slow association. This result demonstrates that the fast association of an IDP can be achieved by stabilizing TC through native/non-native electrostatic interactions, which would allow longer time for an IDP to interact with a target protein to fold and bind.

A Generalized Theory Explains the Anomalous Suns– $V_{{\rm{oc}}}$ Response of Si Heterojunction Solar Cells

Suns– $V_{{\rm{oc}}}$ measurements exclude parasitic series resistance effects and are, therefore, frequently used to study the intrinsic potential of a given photovoltaic technology. However, when applied to a-Si/c-Si heterojunction (SHJ) solar cells, the Suns– V oc curves often feature a peculiar turnaround at high illumination intensities. Generally, this turn-around is attributed to extrinsic Schottky contacts that should disappear with process improvement. In this paper, we demonstrate that this voltage turnaround may be an intrinsic feature of SHJ solar cells, arising from the heterojunction (HJ), as well as its associated carrier-transport barriers, inherent to SHJ devices. We use numerical simulations to explore the full current–voltage ( J–V ) characteristics under different illumination and ambient temperature conditions. Using these characteristics, we establish the voltage and illumination-intensity bias, as well as temperature conditions necessary to observe the voltage turnaround in these cells. We validate our turnaround hypothesis using an extensive set of experiments on a high-efficiency SHJ solar cell and a molybdenum oxide (MoOx) based hole collector HJ solar cell. Our work consolidates Suns– $V_{{\rm{oc}}}$ as a powerful characterization tool for extracting the cell parameters that limit efficiency in HJ devices.

Stability of CIGS solar cells under illumination with damp heat and dry heat: A comparison

Unencapsulated CIGS solar cells were simultaneously exposed to either dry or damp heat combined illumination. In-situ monitoring of their electrical parameters demonstrated a rapid decrease of the efficiency for the solar cells exposed to damp heat plus illumination. This decrease was mainly driven by changes in the shunt resistances, affecting also the open circuit voltage and fill factor, while a minor increase in series resistance was also observed. The solar cells exposed to dry heat plus illumination were almost stable during the exposure.The solar cells were studied before and after exposure in order to investigate their material changes. For the dry heat illumination samples, the visual characteristics remained unchanged, while for the damp heat illumination samples, spots that were likely shunted, were observed. For these solar cells, SIMS showed the migration of sodium, likely leading to changes in the shunt resistance and output voltage. A similar, but less severe migration effect was observed for potassium, so this element might also have a small, but comparable role. Migration of hydroxide, likely caused by water ingression, was also observed and probably affected the conductivity of the ZnO:Al front contact. The migration of sodium and hydroxide was especially strong on the spot locations. These changes were not observed for the dry heat illumination samples. From these experiments, it was concluded that unencapsulated CIGS solar cells can degrade rapidly in the presence of humidity, but in the absence of water, these solar cells were stable even under high temperatures and illumination intensities.

Chronic activation of the D156A point mutant of Channelrhodopsin-2 signals apoptotic cell death: the good and the bad.

Channelrhodopsin-2 (ChR2) has become a celebrated research tool and is considered a promising potential therapeutic for neurological disorders. While making its way into the clinic, concerns about the safety of chronic ChR2 activation have emerged; in particular as the high-intensity blue light illumination needed for ChR2 activation may be phototoxic. Here we set out to quantify for the first time the cytotoxic effects of chronic ChR2 activation. We studied the safety of prolonged illumination on ChR2(D156A)-expressing human melanoma cells as cancer cells are notorious for their resistance to killing. Three days of illumination eradicated the entire ChR2(D156A)-expressing cell population through mitochondria-mediated apoptosis, whereas blue light activation of non-expressing control cells did not significantly compromise cell viability. In other words, chronic high-intensity blue light illumination alone is not phototoxic, but prolonged ChR2 activation induces mitochondria-mediated apoptosis. The results are alarming for gain-of-function translational neurological studies but open the possibility to optogenetically manipulate the viability of non-excitable cells, such as cancer cells. In a second set of experiments we therefore evaluated the feasibility to put melanoma cell proliferation and apoptosis under the control of light by transdermally illuminating in vivo melanoma xenografts expressing ChR2(D156A). We show clear proof of principle that light treatment inhibits and even reverses tumor growth, rendering ChR2s potential tools for targeted light-therapy of cancers.

Rapid Stabilization of High-Performance Multicrystalline P-type Silicon PERC Cells

Light-induced or, more broadly, carrier-induced degradation (CID) in high-performance multicrystalline silicon (HP mc-Si) solar cells remains a serious issue for many manufacturers, and the root cause of the degradation is still unknown. In this paper, the impact of firing temperature on the stability of lifetime test structures is investigated, and it is found that substantial CID can be triggered if peak temperatures exceed approximately 700 °C. We then investigate two pathways to stabilize the performance of industrially produced HP mc-Si passivated emitter rear contact cells which have been fired at CID-activating temperatures (∼740 °C–800 °C) currently required for silver contact formation. The first is a fast-firing approach, whereby it is demonstrated that an additional firing step at a reduced temperature after cell metallization can suppress the extent of ${V_{{\rm{oc}}}}$ degradation by up to 80%. The second approach is the accelerated degradation and subsequent recovery of carrier lifetime through the use of high-intensity illumination during annealing at elevated temperatures. A 30 s process is found to suppress the maximum extent of degradation in ${V_{{\rm{oc}}}}$ by up to 60% and up to 80% for longer processes. Ultimately, the results suggest that a combined approach of fast-firing and a high-intensity-illuminated anneal could achieve the best results in terms of ${V_{{\rm{oc}}}}$ stability.

Highly photostable, reversibly photoswitchable fluorescent protein with high contrast ratio for live-cell superresolution microscopy

Two long-standing problems for superresolution (SR) fluorescence microscopy are high illumination intensity and long acquisition time, which significantly hamper its application for live-cell imaging. Reversibly photoswitchable fluorescent proteins (RSFPs) have made it possible to dramatically lower the illumination intensities in saturated depletion-based SR techniques, such as saturated depletion nonlinear structured illumination microscopy (NL-SIM) and reversible saturable optical fluorescence transition microscopy. The characteristics of RSFPs most critical for SR live-cell imaging include, first, the integrated fluorescence signal across each switching cycle, which depends upon the absorption cross-section, effective quantum yield, and characteristic switching time from the fluorescent "on" to "off" state; second, the fluorescence contrast ratio of on/off states; and third, the photostability under excitation and depletion. Up to now, the RSFPs of the Dronpa and rsEGFP (reversibly switchable EGFP) families have been exploited for SR imaging. However, their limited number of switching cycles, relatively low fluorescence signal, and poor contrast ratio under physiological conditions ultimately restrict their utility in time-lapse live-cell imaging and their ability to reach the desired resolution at a reasonable signal-to-noise ratio. Here, we present a truly monomeric RSFP, Skylan-NS, whose properties are optimized for the recently developed patterned activation NL-SIM, which enables low-intensity (∼100 W/cm(2)) live-cell SR imaging at ∼60-nm resolution at subsecond acquisition times for tens of time points over broad field of view.

Obstacle Detection from Still Images using Improved Background Subtraction Method

Background/Objectives: We propose an approach that aims at improving the current method of obstacle detection so as to improve efficiency, detection rate and running time. Methods/Statistical Analysis: Background subtraction is a technique used in obstacle detection to find out the area of hindrances for traversal or navigation. In this technique two consecutive frame of video is taken for differencing and resultant giving the area in which obstacle is identified. Findings: The current technique has some limitations working under high intensity and change of illumination. We propose a hybrid approach which include merging of gamma correction with background subtraction. This method reduces the level of illumination and works well at different weather conditions. Our proposed method is useful in detection of area of changing objects and would be useful in video surveillance applications.

Protection Against Common Mode Currents on Cables Exposed to HIRF or NEMP

Above deck, cables on naval ships are exposed to high-intensity radiated fields and nuclear electromagnetic pulse (NEMP) that may cause conducted interference and generate electromagnetic fields that exceed the immunity levels of commercially available equipment above and below deck. Exposed cables, such as open power plugs or lighting cables, are modeled and characterized both as a monopole antenna perpendicular to the deck and as a transmission line, representing a cable close to the deck. The placement of an illuminated cable close to the deck is a good protection measure for long cables at low frequencies, which includes NEMP protection. The coupled pulse from a high-intensity NEMP illumination is not expected to cause damage on electric installations. It is shown that for exposed cable length of maximum 25 cm and not placed in the line of sight of transmitters above 400 MHz, no additional protection measures are needed.

Enhanced Ascorbate Regeneration Via Dehydroascorbate Reductase Confers Tolerance to Photo-Oxidative Stress in Chlamydomonas reinhardtii.

The role of ascorbate (AsA) recycling via dehydroascorbate reductase (DHAR) in the tolerance of Chlamydomonas reinhardtii to photo-oxidative stress was examined. The activity of DHAR and the abundance of the CrDHAR1 (Cre10.g456750) transcript increased after moderate light (ML; 750 µmol m-2 s-1) or high light (HL; 1,800 µmol m-2 s-1) illumination, accompanied by dehydroascorbate (DHA) accumulation, decreased AsA redox state, photo-inhibition, lipid peroxidation, H2O2 overaccumulation, growth inhibition and cell death. It suggests that DHAR and AsA recycling is limiting under high-intensity light stress. The CrDHAR1 gene was cloned and its recombinant CrDHAR1 protein was a monomer (25 kDa) detected by Western blot that exhibits an enzymatic activity of 965 µmol min-1 mg-1 protein. CrDHAR1 was overexpressed driven by a HSP70A:RBCS2 fusion promoter or down-regulated by artificial microRNA (amiRNA) to examine whether DHAR-mediated AsA recycling is critical for the tolerance of C. reinahartii cells to photo-oxidative stress. The overexpression of CrDHAR1 increased DHAR protein abundance and enzyme activity, AsA pool size, AsA:DHA ratio and the tolerance to ML-, HL-, methyl viologen- or H2O2-induced oxidative stress. The CrDHAR1-knockdown amiRNA lines that have lower DHAR expression and AsA recycling ability were sensitive to high-intensity illumination and oxidative stress. The glutathione pool size, glutathione:oxidized glutathione ratio and glutathione reductase and ascorbate peroxidase activities were increased in CrDHAR1-overexpressing cells and showed a further increase after high-intensity illumination but decreased in wild-type cells after light stress. The present results suggest that increasing AsA regeneration via enhanced DHAR activity modulates the ascorbate-glutathione cycle activity in C. reinhardtii against photo-oxidative stress.

Differences in stability and repeatability between GaAs and GaAlAs photocathodes

For the applications in vacuum photodetectors and photoinjectors, a crucial limiting factor for conventional GaAs photocathodes is the limited lifetime, depending on the Cs–O activation layer vulnerable to the harmful residual gases. In order to develop a type of GaAs-based photocathode with good stability and repeatability, Cs/O activation and multiple recesiation experiments under the same preparation condition were performed on reflection-mode exponential-doped GaAs and GaAlAs photocathodes grown by metalorganic vapor phase epitaxy, and quantum efficiency and photocurrent decay were measured after activation and recesiation. The experimental results show that the photoemission characteristics on cathode degradation and repeatability are different between GaAs and GaAlAs photocathodes. In an unsatisfactory vacuum system, the operational lifetime for GaAlAs photocathode is nearly twice longer than that for GaAs photocathode after Cs/O activation under a high intensity illumination. After multiple recesiations, the quantum efficiency and operational lifetime for GaAlAs photocathode remain nearly unchanged, while those for GaAs photocathode become lower and lower with the increase of recesiation cycles, which reflects the superiority in stability and repeatability for GaAlAs photocathode in contrast to GaAs photocathode operating in the poor vacuum environment.

Rapid passivation of carrier-induced defects in p-type multi-crystalline silicon

A slow forming carrier-induced degradation effect has previously been reported for p-type multi-crystalline silicon (mc-Si) solar cells and has been observed to be most severe in passivated emitter and rear contact (PERC) designs. The as yet undetermined defect (or defects) responsible for this degradation is typically described as being light-induced. However, in this work we confirm that a directly equivalent degradation also occurs when subjecting a cell to current injection, thus the effect can therefore be more accurately described as being carrier-induced. The defect can take years to form under normal operating conditions, but acceleration of this formation and an apparent subsequent passivation through the use of high intensity illumination at elevated temperatures has recently been demonstrated. In this work we further investigate this approach, analyzing the effects of temperature and time on degradation, regeneration, and resulting stability, as well as the variations in treatment response for mc-Si materials from two different manufacturers. Susceptibility to carrier-induced degradation after 225h of light soaking at 70°C is shown to be reduced by 80% using a rapid, 10s treatment with an illumination intensity of 44.8kw/m2 at 200°C. Stability is shown to further improve by extending treatment time but is reduced with increasing treatment temperature.

Morphology, anatomy, and mycorrhizal fungi colonization in roots of epiphytic orchids of Sempu Island, East Java, Indonesia

Nurfadilah S, Yulia ND, Ariyanti EE. 2016. Morphology, anatomy, and mycorrhizal fungi colonisation in roots of epiphytic orchids of Sempu Island, East Java, Indonesia. Biodiversitas 17: 592-603. Roots of orchids have important role for survival, adaptation, water and nutrient absorption, and as a place of symbiosis with mycorrhizal fungi. The present study aimed to investigate the morphology, anatomy, and mycorrhizal status in roots of orchids of Sempu Island, Indonesia (Ascochilus emarginatus, Taeniophyllum biocellatum, and Thrixspermum subulatum), in relation to their adaptation to their habitat of coastal forests of Sempu Island. These orchids have different morphological characters; Ascochilus emarginatus and Thrixspermum subulatum are leafy orchids, while Taeniophyllum biocellatum is a leafless orchid. The results showed that all orchids have small number of velamen layers (1-2 layers) as an adaptation to the relatively humid condition. Cell wall thickenings of velamen, exodermis, and endodermis are structural adaptation of all orchids to the relatively high intensity of illumination, to reduce water loss because of transpiration. Mycorrhizal fungi colonization which is important for nutrient acquisition occurs in cortical cells. All orchids have differences in their cell shape, size, and specific characters, such as chloroplasts. The leafless Taeniophyllum biocellatum has many chloroplasts in the cortical root cells that support the photosynthesis process, while A. emarginatus and T. subulatum are lack of chloroplasts in their cortical root cells.

Analysis and model delineation of marine microalgae growth and lipid accumulation in flat-plate photobioreactor

A quantitative description of its growth and the “trade-off” between biomass production and lipid accumulation will provide a kinetic insight of the dependency of biomass and components on growth conditions and the interplays between lipid/protein production and N-limitation. The examination of the dependency of Isochrysis galbana growth on initial concentration of sodium nitrate (NaNO3) in a flat-plate photobioreactor (FPPBR) revealed that the maximal lipid 106mgL−1 is produced at 25mgL−1 NaNO3 and whereas the accumulation of biomass, protein and starch increases as NaNO3 increases to 100mgL−1. The analysis and model fitting results indicate that I. galbana growth and production of lipids in a FPPBR can be quantitatively described by Baranyi-Roberts & logistic equation, and Luedeking-Piret model in a satisfactory manner, respectively. 25–75mgL−1 was found to be proper level of NaNO3 to achieve a good trade-off balance to produce both high quantities of biomass and lipids. Based on the predictions of growth model, after culturing middle stationary phase under the high nitrogen medium, switching of culture for algal cells to a nitrogen-free medium and/or high illumination intensity might be preferable strategy to achieve high level accumulation of lipids.

Influence of the formation- and passivation rate of boron-oxygen defects for mitigating carrier-induced degradation in silicon within a hydrogen-based model

A three-state model is used to explore the influence of defect formation- and passivation rates of carrier-induced degradation related to boron-oxygen complexes in boron-doped p-type silicon solar cells within a hydrogen-based model. The model highlights that the inability to effectively mitigate carrier-induced degradation at elevated temperatures in previous studies is due to the limited availability of defects for hydrogen passivation, rather than being limited by the defect passivation rate. An acceleration of the defect formation rate is also observed to increase both the effectiveness and speed of carrier-induced degradation mitigation, whereas increases in the passivation rate do not lead to a substantial acceleration of the hydrogen passivation process. For high-throughput mitigation of such carrier-induced degradation on finished solar cell devices, two key factors were found to be required, high-injection conditions (such as by using high intensity illumination) to enable an acceleration of defect formation whilst simultaneously enabling a rapid passivation of the formed defects, and a high temperature to accelerate both defect formation and defect passivation whilst still ensuring an effective mitigation of carrier-induced degradation.

Acceleration and mitigation of carrier-induced degradation in p-type multi-crystalline silicon

Recently, a new carrier-induced defect has been reported in multi-crystalline silicon (mc-Si), and has been shown to be particularly detrimental to the performance of passivated emitter and rear contact (PERC) cells. Under normal conditions, this defect can take years to fully form. This Letter reports on the accelerated formation and subsequent passivation of this carrier-induced defect through the use of high illumination intensity and elevated temperatures resulting in passivation within minutes. The process was tested on industrial mc-Si PERC solar cells, where degradation after a 100 hour stability test was suppressed to only 0.1% absolute compared to 2.1% for non-treated cells. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Investigations on accelerated processes for the boron–oxygen defect in p-type Czochralski silicon

As new solar cell architectures are developed with superior surface passivation, the boron–oxygen defect becomes an increasingly significant limitation on device performance for p-type Czochralski silicon solar cells. This has led to research into methods of permanently deactivating the recombination activity associated with the defect and how these might be implemented in an industrial environment. While the ability to passivate this defect at temperatures below 500K has been widely reported in the literature, recent results from the authors have demonstrated the ability to achieve near complete passivation of this defect at temperatures in excess of 600K under high intensity illumination. This ability to passivate the defect at higher temperatures than previously reported may be explained by an increase in the rate of defect passivation, or alternately, by an increase in the defect formation rate. This paper explores the dependence of defect passivation upon illumination intensity, temperature and the initial state of the defects. Evidence is presented to suggest that high intensity illumination does not significantly increase the rate of passivation, but rather greatly enhances the defect formation rate. Based upon this understanding it is demonstrated how a 10s process under high intensity illumination may be used to completely eliminate the impact of the boron–oxygen defect on solar cell performance, with no requirement for prior defect formation.

ADVANCED IMAGING. Extended-resolution structured illumination imaging of endocytic and cytoskeletal dynamics.

Super-resolution fluorescence microscopy is distinct among nanoscale imaging tools in its ability to image protein dynamics in living cells. Structured illumination microscopy (SIM) stands out in this regard because of its high speed and low illumination intensities, but typically offers only a twofold resolution gain. We extended the resolution of live-cell SIM through two approaches: ultrahigh numerical aperture SIM at 84-nanometer lateral resolution for more than 100 multicolor frames, and nonlinear SIM with patterned activation at 45- to 62-nanometer resolution for approximately 20 to 40 frames. We applied these approaches to image dynamics near the plasma membrane of spatially resolved assemblies of clathrin and caveolin, Rab5a in early endosomes, and α-actinin, often in relationship to cortical actin. In addition, we examined mitochondria, actin, and the Golgi apparatus dynamics in three dimensions.

Abnormal behavior of threshold voltage shift in bias-stressed a-Si:H thin film transistor under extremely high intensity illumination.

We report on the unusual behavior of threshold voltage turnaround in a hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT) when biased under extremely high intensity illumination. The threshold voltage shift changes from negative to positive gate bias direction after ∼30 min of bias stress even when the negative gate bias stress is applied under high intensity illumination (>400 000 Cd/cm(2)), which has not been observed in low intensity (∼6000 Cd/cm(2)). This behavior is more pronounced in a low work function gate metal structure (Al: 4.1-4.3 eV), compared to the high work function of Cu (4.5-5.1 eV). Also this is mainly observed in shorter wavelength of high photon energy illumination. However, this behavior is effectively prohibited by embedding the high energy band gap (∼8.6 eV) of SiOx in the gate insulator layer. These imply that this behavior could be originated from the injection of electrons from gate electrode, transported and trapped in the electron trap sites of the SiNx/a-Si:H interface, which causes the shift of threshold voltage toward positive gate bias direction. The results reported here can be applicable to the large-sized outdoor displays which are usually exposed to the extremely high intensity illumination.

Influence of porous silicon formation on the performance of multi-crystalline silicon solar cells

The effect of formation of porous silicon on the performance of multi-crystalline silicon (mc-Si) solar cells is presented. Surface treatment of mc-Si solar cells was performed by electrochemical etching in HF-based solution. The effect of etching is viewed through scanning electron microscope (SEM) photographs that indicated the formation of a porous layer on the surface. Total reflection spectroscopy measurements on solar cells revealed reduced reflection after etching. In order to demonstrate the effect of this porous layer on the solar cell performance, illumination-dependent j–V characteristics and spectral response measurements were performed and analysed before and after etching. At all illumination intensities, short-circuit current density and open-circuit voltage values for the etched solar cell were higher than those before etching, whereas fill factor values were lower for the etched cell at high illumination intensities. An interpretation of these findings is presented.