Design of Plasmonic Nanoparticles for Efficient Subwavelength Light Trapping in Thin-Film Solar Cells

This paper explores geometry-sensitive scattering from plasmonic nanoparticles deposited on top of a thin-film amorphous silicon solar cell to enhance light trapping in the photo-active layer. Considering the nanoparticles as ideal spheroids, the broadband optical absorption by the silicon layer is analyzed and optimized with respect to the nanoparticle aspect ratio in both the cases of resonant (silver) and nonresonant (aluminum) plasmonic nanostructures. It is demonstrated how the coupling of sunlight with the semiconductor can be improved through tuning the nanoparticle shape in both the dipolar and multi-polar scattering regimes, as well as discussed how the native oxide shell formed on the nanospheroid surface after the prolonged action of air and moisture affects the light trapping in the active layer and changes the photocurrent generation by the solar cell.     

Plasmon-Enhanced Light Trapping to Improve Efficiency of TiO2 Nanorod-Based Dye-Sensitized Solar Cell

Localized surface plasmon resonance incurred by silver nanoparticles is used to enhance the photoelectric conversion efficiency of a TiO₂ nanorod-based dye-sensitized solar cell (DSSC). Improved light transmission is observed experimentally in silver nanoparticle-coated FTO glass. The transmission data are used to explore the effect on electrical parameters of DSSC using theoretical model. Current density increased from 11.7 to 12.34 mA/cm² and open-circuit voltage increased from 704 to 709.5 mV. Overall efficiency enhancement of 6.67 % is observed in TiO₂ nanorod-based DSSC due to plasmon-induced light trapping.     

Optimization of Dielectric-Coated Silver Nanoparticle Films for Plasmonic-Enhanced Light Trapping in Thin Film Silicon Solar Cells

Surface plasmonic-enhanced light trapping from metal nanoparticles is a promising way of increasing the light absorption in the active silicon layer and, therefore, the photocurrent of the silicon solar cells. In this paper, we applied silver nanoparticles on the rear side of polycrystalline silicon thin film solar cell and systematically studied the dielectric environment effect on the absorption and short-circuit current density (Jsc) of the device. Three different dielectric layers, magnesium fluoride (MgF₂, n?=?1.4), tantalum pentoxide (Ta₂O₅, n?=?2.2), and titanium dioxide (TiO₂, n?=?2.6), were investigated. Experimentally, we found that higher refractive index dielectric coatings results in a redshift of the main plasmonic extinction peak and higher modes were excited within the spectral region that is of interest in our thin film solar cell application. The optical characterization shows that nanoparticles coated with highest refractive index dielectric TiO₂ provides highest absorption enhancement 75.6 %; however, from the external quantum efficiency characterization, highest short-circuit current density Jsc enhancement of 45.8 % was achieved by coating the nanoparticles with lower refractive index MgF₂. We also further optimize the thickness of MgF₂ and a final 50.2 % Jsc enhancement was achieved with a 210-nm MgF₂ coating and a back reflector.     

Tuning of Light Trapping and Surface Plasmon Resonance in Silver Nanoparticles/c-Si Structures for Solar Cells

In this work, we investigate silver (Ag) nanoparticle-related plasmonic effect on light absorption in Si substrate. Ag nanoparticles (Ag-NPs) deposited on top of Si were used to capture and couple incident light into these structures by forward scattering. We demonstrate that we can control nanoparticle size and shape while varying deposition time and annealing parameters. By the increase of the total time of the reaction process, morphology of Ag-NPs evolutes affecting the number and the width of surface plasmon resonance peaks, whereas for changed annealing parameters (temperature and time), the effect is more pronounced on the broadening and the position of peaks. Specific morphology of Ag-NPs can exhibit an interesting enhancement of optical properties which enables plasmon-related application in photovoltaic solar cells.     

Asymmetric Binary Plasmon Resonator Arrays for Perfect Trapping of Light

We propose to achieve perfect trapping of light with asymmetric binary plasmon resonator arrays on metal substrates, in which antisymmetrically coupled resonance modes are excited in each subwavelength period to eliminate any leaky radiation. The specific structure in the study is an ultrathin binary metal stripe array on a flat metal substrate interspaced with a dielectric layer. The antiphase resonance modes are excited underneath the binary metal stripes in each period, resulting in perfect trapping of light under appropriate difference of the metal stripe widths. The trapped light is fully absorbed by metals, accompanied with an improved enhancement of the local field compared to those in symmetric structures with equal metal stripe widths. The work suggests a new way in designing optical metamaterials to manipulate light for enhanced light-matter interactions.     

The Solar Action Spectrum of Photosystem II Damage

The production of oxygen and the supply of energy for life on earth rely on the process of photosynthesis using sunlight. Paradoxically, sunlight damages the photosynthetic machinery, primarily photosystem II (PSII), leading to photoinhibition and loss of plant performance. However, there is uncertainty about which wavelengths are most damaging to PSII under sunlight. In this work we examined this in a simple experiment where Arabidopsis (Arabidopsis thaliana) leaves were exposed to different wavelengths of sunlight by dispersing the solar radiation across the surface of the leaf via a prism. To isolate only the process of photodamage, the repair of photodamaged PSII was inhibited by infiltration of chloramphenicol into the exposed leaves. The extent of photodamage was then measured as the decrease in the maximum quantum yield of PSII using an imaging pulse amplitude modulation fluorometer. Under the experimental light conditions, photodamage to PSII occurred most strongly in regions exposed to ultraviolet (UV) or yellow light. The extent of UV photodamage under incident sunlight would be greater than we observed when one corrects for the optical efficiency of our system. Our results suggest that photodamage to PSII under sunlight is primarily associated with UV rather than photosynthetically active light wavelengths.Plants absorb sunlight to power the productive photochemical reactions of photosynthesis. Absorption of sunlight may also lead to deleterious photochemistry that damages the photosynthetic machinery. The PSII protein complex is important in this regard as it seems to be most susceptible to photodamage that results in photoinhibition and ultimately suppresses photosynthetic CO₂ assimilation, growth, and productivity (Long et al., 1994; Takahashi and Murata, 2008). Although plants have photoprotection mechanisms (Niyogi, 1999) and can effectively repair photodamaged PSII through the PSII repair cycle (Aro et al., 1993), photoinhibition still occurs under stressful environmental conditions (Nishiyama et al., 2006; Murata et al., 2007; Takahashi and Murata, 2008).The onset of photoinhibition is strongly correlated with the absorption of excessive excitation energy for photosynthesis. Therefore, photodamage to PSII was most readily assumed to be attributed to the excess light absorbed by photosynthetic pigments (Melis, 1999). However, the extent of photodamage that is measured under conditions where the repair of photodamaged PSII is prevented by inhibiting chloroplast protein synthesis (i.e. lincomycin or chloramphenicol) is directly proportional to the intensity of light (Mattoo et al., 1984; Tyystjärvi and Aro, 1996; Nishiyama et al., 2001, 2004; Allakhverdiev and Murata, 2004; Chow et al., 2005). Furthermore, recent studies have demonstrated that interruption of the Calvin cycle (Hakala et al., 2005; Takahashi and Murata, 2005; Takahashi et al., 2007) and inhibition of electron transfer between Q_A and Q_B (Jegerschöld et al., 1990; Kirilovsky et al., 1994; Allakhverdiev et al., 2005) have no effect on the rate of photodamage to PSII, but in fact cause inhibition of the repair of photodamaged PSII due to suppression of the de novo synthesis of PSII proteins (Allakhverdiev et al., 2005; Takahashi and Murata, 2005, 2006). Thus, photodamage to PSII is paradoxically not associated with the excess light absorbed by photosynthetic pigments (Nishiyama et al., 2006; Murata et al., 2007; Takahashi and Murata, 2008).Studies of the effect of monochromatic light on the photodamage process have suggested that photodamage to PSII primarily occurs at the manganese cluster of the oxygen-evolving complex (OEC) through a direct photoexcitation of manganese (Hakala et al., 2005; Ohnishi et al., 2005). Release of manganese ions (Mn²⁺) from thylakoid membranes is accompanied by photodamage to PSII (Hakala et al., 2005; Zsiros et al., 2006), suggesting that disruption of the manganese cluster upon absorption of light might be a primary event in photodamage. It is likely that the reaction center of PSII is secondarily damaged by light absorbed by photosynthetic pigments after inactivation of the OEC (Hakala et al., 2005; Ohnishi et al., 2005), if an alternative electron transfer donor from lumenal ascorbate is not available (Mano et al., 2004; Tóth et al., 2009). These findings have lead to a recent photodamage model called the manganese (or two-step; Ohnishi et al., 2005) mechanism of photoinhibition (Tyystjärvi, 2008).Studies of the action spectrum of photodamage to PSII have shown that UV damages PSII more effectively than visible light (Jones and Kok, 1966; Jung and Kim, 1990; Hakala et al., 2005; Ohnishi et al., 2005). Thus, under identical light intensity, UV is the most damaging wavelength to PSII. However, inferring damage under natural sunlight is not straight forward as there is a need to account for the spectral distribution and intensity of sunlight. It is unclear which wavelengths of sunlight are most damaging to PSII and we cannot discount the premise that significant primary photodamage to PSII is caused by light absorbed by photosynthetic pigments (Vass and Cser, 2009). To identify which wavelengths of sunlight are most damaging to PSII, sunlight was spectrally dispersed via a prism onto an Arabidopsis (Arabidopsis thaliana) leaf infiltrated with chloramphenicol and decrease in the maximum quantum yield of PSII (F_v/F_m) was measured using an imaging pulse amplitude modulation (PAM) fluorometer. This simple but powerful approach revealed the in vivo spectral dependence of photodamage that had two peaks at UV and yellow wavelengths. Since the spectral efficiency of our optical system decreased below 400 nm, we calculated photodamage to PSII under incident sunlight. Our results show that photodamage to PSII was primarily associated with UV wavelengths and secondarily with yellow light wavelengths. This finding indicates that photodamage to PSII is less associated with light absorbed by photosynthetic pigments under sunlight and suggest that most of photodamage to PSII is potentially avoidable during photosynthesis.     

Action Spectrum in Ultraviolet and Blue Light Region for the Inhibition of Red-Light-Induced Spore Germination in Adiantum capillus-veneris L.

The action spectrum for the inhibition of red-light-inducedgermination of spores in the fern Adiantum capillus-veneriswas determined between 250 and 500 nm using the Okazaki largespectrograph. When monochromatic lights were given after red-lightirradiation, two prominent peaks for inhibition of spore germinationwere observed at 275 and 440 nm and a minor peak at ca. 390nm. ² Permanent address: Department of Botany, Faculty of Science,University of Tokyo, Hongo, Tokyo 113, Japan.     

Light Trapping Effect in Wing Scales of Butterfly Papilio peranthus and Its Simulations

Broadband light trapping effect and arrays of sub-wavelength textured structures based on the butterfly wing scales are applicable to solar cells and stealth technologies. In this paper, the fine optical structures in wing scales of butterfly Papilio peranthus, exhibiting efficient light trapping effect, were carefully examined. First, the reflectivity was measured by reflectance spectrum. Field Emission Scanning Electronic Microscope (FESEM) and Transmission Electron Microscope (TEM) were used to observe the coupling morphologies and structures of the scales. Then, the optimized 3D model of the coupling structure was created combining Scanning Electron Microscope (SEM) and TEM data. Afterwards, the mechanism of the light trapping effect of these structures was analyzed by simulation and theoretical calculations. A multilayer nano-structure of chitin and air was found. These structures are effective in increasing optical path, resulting in that most of the incident light can be trapped and adsorbed within the structure at last. Furthermore, the simulated optical results are consistent with the experimental and calculated ones. This result reliably confirms that these structures induce an efficient light trapping effect. This work can be used as a reference for in-depth study on the fabrication of highly efficient bionic optical devices, such as solar cells, photo detectors, high-contrast, antiglare, and so forth.     

Spectrally Selective Transformations of Solar Radiation by Retinal Photoreceptors in the Control of the Circadian Rhythm of the Human Body throughout an 11-Year Cycle of Solar Activity

Biophysics - Abstract—The round-the-day effect of solar radiation on photoreceptors of the retina of the eye and its role in the control of the circadian rhythm of the human body within an...     

Influence of Constant Light and Darkness,Light Intensity,and Light Spectrum on Plasma Melatonin Rhythms in Senegal Sole

Light is the most important synchronizer of melatonin rhythms in fish. This paper studies the influence of the characteristics of light on plasma melatonin rhythms in sole. The results revealed that under long‐term exposure to constant light conditions (LL or DD), the total 24 h melatonin production was significantly higher than under LD, but LL and DD conditions influenced the rhythms differently. Under LL, melatonin remained at around 224 pg/ml throughout the 24 h, while under DD a significant elevation (363.6 pg/ml) was observed around the subjective evening. Exposure to 1 h light pulses at MD (mid‐dark) inhibited melatonin production depending on light intensity (3.3, 5.3, 10.3, and 51.9 µW/cm²). The light threshold required to reduce nocturnal plasma melatonin to ML (mid‐light) values was 5.3 µW/cm². Melatonin inhibition by light also depended on the wavelength of the light pulses: while a deep red light (λ>600 nm) failed to reduce plasma melatonin significantly, far violet light (λ_max=368 nm) decreased indoleamine's concentration to ML values. These results suggest that dim light at night (e.g., moonlight) may be perceived and hence affect melatonin rhythms, encouraging synchronization to the lunar cycle. On the other hand, deep red light does not seem to inhibit nocturnal melatonin production, and so it may be used safely during sampling at night.     

紫外光源及太阳UV-B辐射的模拟实验

介绍了用于UV-B生物学效应研究的几种常见光源,对如何利用选择性薄膜获得理想的UV-B波段的光谱,进而能较真实模拟平流层O3耗损所导致的近地表面太阳UV-B辐射的增强,以及在野外进行UV-B模拟研究时,紫外荧光灯管的排列方式等进行了分析讨论。介绍并讨论了当前UV-B辐射实验的各种方法,并就各实验设计的注意事项和安全操作等提出了建议。     

Full Coverage of the Solar Spectrum and Beyond Using All-Manganese Plasmonic Shell Array

Plasmonics - In this paper, shell-shaped truncated pyramidal unit cells have been used in the design of solar cells. The shells are formed by manganese (Mn) transition metal which has very similar...     

Action Spectrum in the Ultraviolet Region for Phototropism of Bryopsis Rhizoids

The phototropic response of the rhizoid of the marine coenocyticgreen alga Bryopsis plumosa to ultraviolet light (250–350nm) was investigated. The rhizoid exhibited negative bendingthat was due to bulging upon absorption of light in the UV region,as well as in the visible region, of the spectrum. The negativebending might not be a result of the inhibition of growth onthe irradiated side of the apical hemisphere by UV irradiationbecause growth inhibition was observed after bending had reacheda maximum within one to two hours. The action spectrum obtainedfrom fluence rate-response curves had a pronounced peak at 260nm and a small peak at 310 nm. The quantum effectiveness at260 nm was about five times that in the visible region. Phenylaceticacid (PAA), a potent inhibitor of flavin photoreactions, inhibitedthe phototropic response to both UV light and blue light withoutany obvious effect on tip growth. The inhibition of the phototropicresponse to blue light by PAA was partially overcome by rinsingthe alga with riboflavin-containing medium, which result suggeststhe involvement of flavins in the phototropism of Bryopsis rhizoids. (Received February 6, 1995; Accepted June 19, 1995)     

Action Spectrum of Light Pulse-Induced Membrane Depolarization in Pulvinar Motor Cells of Phaseolus

In addition to circadian changes in the membrane potential andleaf movement, light applied to the pulvinus causes changesin both the membrane potential and the pulvinar movement inPhaseolus vulgaris L. Even after a short pulse of light, a transientdepolarization of the membrane occurs and leaf movement is observed.Decreases of turgor pressure of the motor cells are always precededby the depolarization. The direction of the leaf movement canbe explained by the decrease of turgor pressure in the motorcells on the irradiated side of the pulvinus. Using the OkazakiLarge Spectrograph at the National Institute for Basic Biology,we determined the action spectrum of the membrane depolarizationinduced by light pulses (30 s) in motor cells of Phaseolus.The pulvinus was left exposed to air during measurement of themembrane potential with microelectrodes. The action spectrumobtained was in the range of 300 to 730 nm. It had the highestpeak at 460 nm with lower peaks at 380 nm and 420 nm. Almostno sensitivity was observed at wavelengths shorter than 360nm and longer than 520 nm. Red and far-red light had no effecton the depolarization of the motor cell. The features of theaction spectrum are almost the same as those of the Blue-Typeresponse in plants. (Received January 9, 1997; Accepted February 14, 1997)     

The Heterochromatic ABO Locus May Overlap with the Region Containing Repeats Encompassing Mobile Elements andStellate Genes on the X Chromosome of Drosophila melanogaster

A deficiency of certain heterochromatic regions (ABO loci) of various chromosomes dramatically distorts the early embryo development in the progeny of females carrying mutation in the abnormal oocyte (abo) gene, which is located in euchromatin of chromosome 2. One ABO locus (X-ABO) is in X-heterochromatin distal to the nucleolus organizer. A cluster of the Stellate repeats is located in the same heterochromatic block. Deletions of various fragments from distal heterochromatin were tested for the effect on expression of the abo mutation. The X-ABO locus was assigned to X-chromosomal heterochromatin segment h26 and may include repeats consisting mostly of mobile elements and defective Stellate copies. A major part of the regular Stellate tandem repeats proved to be distal of the X-ABO locus.     

Contribution of LSP Effect to Light Absorption in Thin-Film Crystalline Silicon Solar Cells

Introducing periodic Ag gratings in the rear side of thin-film silicon excites localized surface plasmon (LSP) and Fabry-Perot (FP) effect. These two effects as well as an intrinsic one pass through absorption overlay together and all contribute to the light absorption in silicon. On the basis of electromagnetic field’s linear superposition, the absorptivity caused by LSP effect is separated from the overall absorptivity of a 500-nm-thick silicon and quantized by short current density. Finite difference time domain (FDTD) calculations were performed to obtain the absorptivity of silicon with different Ag grating parameters. The contribution of LSP effect to the light absorption is evaluated by photocurrent ratio and investigated under different Ag grating parameters. It is found that, as LSP effect is excited most intensively, the light absorption of silicon will also be enhanced extremely. By careful design, the overall short current density of silicon is optimized up to 25.4 mA/cm², where the contribution of LSP effect accounts for 38.6 %. Comparing to 14.5 mA/cm² for a reference silicon stack, it increases up to almost 75 %. These results may give design suggestions in implementation of plasmonic solar cell as high efficiency devices.     

Influences of Nanostructure Arrays on Light Absorption in Amorphous Silicon Thin-Film Solar Cells

By means of finite-difference time-domain (FDTD) numerical method, we investigate the possibility to enhance the light absorption in solar cells by employing different nanostructures. The solar cells are made of 100-nm-thick amorphous silicon (α-Si). The impacts of gold nanohole arrays, dielectric nanosphere arrays, and gold nanoparticle arrays on the light absorption are simulated, compared, and analyzed. The results show that gold nanohole arrays functioning as the back reflective layer, dielectric nanosphere arrays, and gold nanoparticle arrays can significantly enhance the light absorption for the solar cells, and the former two can increase the short-circuit current by more than 40 %, showing a great potential to improve the utilization efficiency of solar energy.