Surface Plasmon Enhancement of Optical Absorption in Thin-Film Silicon Solar Cells

Strong electromagnetic field enhancement that occurs under conditions of the surface plasmon excitation in metallic nanoparticles deposited on a semiconductor surface is a very efficient and promising tool for increasing the optical absorption within semiconductor solar cells and, hence, their photocurrent response. The enhancement of the optical absorption in thin-film silicon solar cells via the excitation of localized surface plasmons in spherical silver nanoparticles is investigated. Using the effective medium model, the effect of the nanoparticle size and the surface coverage on that enhancement is analyzed. The optimum configuration and the nanoparticle parameters leading to the maximum enhancement in the optical absorption and the photocurrent response in a single p-n junction silicon cell are obtained. The effect of coupling between the silicon layer and the surface plasmon fields on the efficiency of the above enhancement is quantified as well.     

Effect of solar ultraviolet radiation on growth in the marine macroalga Dictyota dichotoma (Phaeophyceae) at Helgoland and its ecological consequences

At Helgoland, in the North Sea, growth of the high sublittoral brown macroalga Dictyota dichotoma (Hudson) Lamoroux was examined in October (the time of tetraspore release) in an outdoor tank by exposing 2-day-old germlings to four solar radiation treatments achieved with different filter materials or an additional artificial light source: photosynthetically active radiation (PAR; 395–700 nm), PAR plus ultraviolet (UV)-A (320–700 nm), full solar spectrum, or solar spectrum plus artificial UV radiation (UVR). Based on length measurements over a period of 3 weeks, the growth rate in germlings strongly decreased in conditions with UVR compared to PAR: by 14% under PAR+UV-A, by 31% under the full solar spectrum and by 65% with additional UVR. Although growth rates of germlings under UVR were reduced mainly in the first week, the plants did not regain the size of the untreated plants even after 9 weeks. Regardless of the exposure, no defects in morphology or anatomy including the exposed apical meristem were detected, except for a reduction in cell division rates perhaps due to additional cost for photoprotective or repair mechanisms. Depending on the actual position of D. dichotoma plants in the natural habitat, individuals in high positions receive substantial amounts of the more harmful UV-B while those lower down might only receive UV-A during part of the day, thus the effect of UV-B on the growth of D. dichotoma will depend on its position in the field. The effects of tidal variation of the light climate and the implications of our results for the zonation of D. dichotoma are discussed. Received in revised form: 6 July 2000 Electronic Publication     

Infiltration by inflammatory cells required for solar-simulated ultraviolet radiation enhancement of skin tumor growth

In this study we compared the effects of subinflammatory and inflammatory doses of solar-simulated ultraviolet (UV) radiation on enhancement of skin tumor growth, sensitization to haptens and cellular changes within the epidermis of C3H/HeN mice. Tumors transplanted into mice 3 days after exposure to inflammatory, but not subinflammatory, doses of UV radiation had a higher growth rate than those tumors inoculated into unirradiated control mice. Both doses of UV radiation suppressed the induction of contact hypersensitivity and induced tolerance when hapten was painted onto the skin 3 days after irradiation. Skin exposed to the higher, but not the lower, dose of UV radiation contained significantly increased numbers of CD11b+, CD45+ MHC class II- and CD45+ MHC class II(hi) inflammatory cells 3 days post-irradiation. The immunosuppression correlated with a reduction in Langerhans cells and dendritic epidermal T cells. Collectively, this suggests that suppression to contact sensitizers is due to the UV radiation effects on Langerhans cells and dendritic epidermal T cells. While these effects may also suppress the induction of anti-tumor immunity, at higher doses of UV radiation inflammatory cells may enhance tumor growth by a non-immunological mechanism.     

Keratinocytes Control the Proliferation and Differentiation of Cultured Epidermal Melanocytes from Ultraviolet Radiation B‐Induced Pigmented Spots in the Dorsal Skin of Hairless Mice

Long‐term exposure of ultraviolet radiation B (UVB)‐induced pigmented spots in the dorsal skin of hairless mice of Hos:(HR‐1 X HR//De) F₁. Previous study showed that the proliferative and differentiative activities of cultured epidermal melanoblasts//melanocytes from UVB‐induced pigmented spots increased with the development of the pigmented spots. To determine whether the increase in the proliferative and differentiative activities of epidermal melanoblasts//melanocytes was brought about by direct changes in melanocytes, or by indirect changes in surrounding keratinocytes, pure cultured melanoblasts//melanocytes and keratinocytes were prepared and co‐cultured in combination with control and irradiated mice in a serum‐free culture medium. Keratinocytes from irradiated mice stimulated the proliferation and differentiation of both neonatal and adult non‐irradiated melanoblasts//melanocytes more greatly than those from non‐irradiated mice. In contrast, both non‐irradiated and irradiated adultmelanocytes proliferated and differentiated similarly when they were co‐cultured with irradiated adult keratinocytes. These results suggest that the increased proliferative and differentiative activities of mouse epidermal melanocytes from UVB‐induced pigmented spots are regulated by keratinocytes, rather than melanocytes.     

Sequence-specific DNA damage induced by ultraviolet A-irradiated folic acid via its photolysis product

DNA damage mediated by photosensitizers participates in solar carcinogenesis. Fluorescence measurement and high-performance liquid chromatography analysis demonstrated that photoirradiated folic acid, one of the photosensitizers in cells, generates pterine-6-carboxylic acid (PCA). Experiments using 32P-labeled DNA fragments obtained from a human gene showed that ultraviolet A-irradiated folic acid or PCA caused DNA cleavage specifically at consecutive G residues in double-stranded DNA after Escherichia coli formamidopyrimidine-DNA glycosylase or piperidine treatment. The amount of 8-oxo-7,8-dihydro-2(')-deoxyguanosine formed through this DNA photoreaction in double-stranded DNA exceeded that in single-stranded DNA. Kinetic studies suggested that DNA damage is caused mainly by photoexcited PCA generated from folic acid rather than by folic acid itself. In conclusion, photoirradiated folic acid generates PCA, which induces DNA photooxidation specifically at consecutive G residues through electron transfer. Excess intake of folic acid supplements may increase a risk of skin cancer by solar ultraviolet light.     

Comparisons of the polar lipid and pigment profiles of two solar salterns located in Newark, California, U.S.A., and Eilat, Israel

The whole community pigments and lipids have been examined during a 5-year period in two commercial solar salterns located in the United States and in Israel. There were significant differences in the complexity of the lipid and pigment patterns within the California saltern system, and these differences were not consistent over the sampling period despite examination of ponds with the same salinity. The solar saltern system in Eilat, Israel, showed greater consistency during this sampling period and compared directly with previous studies. The complexity of the saltern in Newark, California, could be explained on the basis of the prevailing weather conditions (cooler and more rainfall) and the nutrient-enriched source water. The Eilat saltern, however, has an oligotrophic water source and has a considerably warmer and drier climate. This difference resulted in more diverse and more complex pigment and lipid patterns and presumably microbial populations in the Newark, California, plant than in the saltern in Eilat, Israel. Received: December 10, 1999 / Accepted: April 6, 2000     

Attraction of stink bugs to rocket traps with different combinations of wing and landing board color

The stink bugs, Halyomorpha halys and Riptortus pedestris, are two of the most economically important pests of leguminous crops and fruits in Korea. Here we present the results from a field monitoring test that evaluated the effect of variation in rocket trap type and color on stink bugs captures. We tested various types of rocket traps, along with wing combinations and landing boards of various colors. The test was run in soybean fields in Miryang, Korea. We developed a modified rocket trap intended to enhance the capture efficacy of stink bugs. We evaluated traps including (1) yellow rocket trap with a solar fan and blue LED lamp, (2) a yellow trap with solar fan but no light, (3) rocket traps with black, green, yellow, white, red, brown, and blue color stimuli, (4) different color combinations of trap wings, and (5) traps with a landing board were evaluated. Our results showed that yellow winged rocket traps with solar fans and blue LED lamps attracted significantly more stink bug species than other traps, in both soybean fields. Use of these improved traps such as a yellow trap with a solar fan and blue LED lamp, and a yellow trap with a solar fan would therefore enhance the monitoring and capture of stink bugs in diversified agro-ecological landscapes. The potential use of traps with a specific hue, combination of features, and modifications to monitor stink bugs accurately is discussed. Continuing improvements to traps to meet the demands of a changing pest landscape and agricultural mechanization are needed.     

Making Record-efficiency SnS Solar Cells by Thermal Evaporation and Atomic Layer Deposition

Tin sulfide (SnS) is a candidate absorber material for Earth-abundant, non-toxic solar cells. SnS offers easy phase control and rapid growth by congruent thermal evaporation, and it absorbs visible light strongly. However, for a long time the record power conversion efficiency of SnS solar cells remained below 2%. Recently we demonstrated new certified record efficiencies of 4.36% using SnS deposited by atomic layer deposition, and 3.88% using thermal evaporation. Here the fabrication procedure for these record solar cells is described, and the statistical distribution of the fabrication process is reported. The standard deviation of efficiency measured on a single substrate is typically over 0.5%. All steps including substrate selection and cleaning, Mo sputtering for the rear contact (cathode), SnS deposition, annealing, surface passivation, Zn(O,S) buffer layer selection and deposition, transparent conductor (anode) deposition, and metallization are described. On each substrate we fabricate 11 individual devices, each with active area 0.25 cm². Further, a system for high throughput measurements of current-voltage curves under simulated solar light, and external quantum efficiency measurement with variable light bias is described. With this system we are able to measure full data sets on all 11 devices in an automated manner and in minimal time. These results illustrate the value of studying large sample sets, rather than focusing narrowly on the highest performing devices. Large data sets help us to distinguish and remedy individual loss mechanisms affecting our devices.     

Motility and orientation of a dinoflagellate, Gymnodinium, impaired by solar and ultraviolet radiation

Abstract The effects of solar and artificial ultraviolet radiation on the motility and orientation of the dinoflagellate Y-100 were studied. The cells show a weak photokinesis but a pronounced phototaxis which is consistently positive between 1 and 100 klx (= 4 mW m⁻² to 400 mW m⁻²); the precision of orientation increases with the fluence rate. Unfiltered solar radiation as well as artificial ultraviolet radiation reduce the percentage of motile cells increasingly with exposure time but the velocity of the still motile cells is less affected. Unirradiated control cells show a negative gravitaxis. After short exposure to solar or artificial ultraviolet radiation the precision of gravitaxis decreases and after prolonged exposure the cells start to actively move downward in the water column (positive gravitaxis). Phototaxis is also strongly impaired by ultraviolet radiation.     

Phenological influences on the albedo of prairie grassland and crop fields

 The albedo of land surfaces is strongly affected by transient surface conditions. For a vegetated surface, albedo can change with soil moisture, fractional canopy cover, and plant phenology as well as solar zenith angle (θ_s). In this study, the relationships between albedo and plant phenology in prairie grassland and agricultural crops were examined by removing the effect of variations in θ_s. Albedos were evaluated at a constant θ_s, which was assigned to be 20° in this study. For days with a minimum θ_s larger than 20°, a polynomial function that relates albedos to θ_s was derived and applied to estimate the albedos at 20°. After the removal of θ_s variations, the observed albedos of grassland at the Konza Prairie showed a linearly decreasing trend from spring to winter due to prairie phenology. The observed albedo of a maize field showed a clear increase from seedling to peak green stage, except when drought caused a decrease in near-infrared reflectance. The observed albedos of a winter wheat field showed an uninterrupted decrease from peak green to harvesting stage. Received: 30 May 1998 / Accepted 15 July1998