1,720,958 research outputs found
Plasmonic and Biomimetic light-trapping for photovoltaics
No full textThe challenge when applying photonics to photovoltaics is the need to provide broadband, multiple-angle solutions to problems and both plasmonics and biomimetics offer broadband approaches to reducing reflection and enhancing light-trapping. Over millions of years nature has optimised nanostructures to create black, transparent, white and mirrored surfaces, the antireflective “moth-eye” structures are perhaps the best known of these biophotonic materials. In this paper we use simulated and experimental studies to illustrate how careful optimisation of nanoscale features is required to ensure the optimum match between reflectivity, spectral bandwidth and device quantum efficiencies. In the case of light-trapping by plasmonic scattering there is more room for design and specific spectral regions can be targeted by precise control of the size, shape and density of particular metal nanoparticles. We describe how the best opportunity for plasmonics within inorganic solar cells appears to be enhanced light-trapping of near-band edge photons
Optical characterisation of a spectrally tunable plasmonic reflector for application in thin film silicon solar cells
No full textWe have investigated the interaction between a random two-dimensional array of Ag islands near a Ag reflector, with the aim of producing a plasmonic back reflector structure with high diffuse reflectivity in the near-infrared, 600–1100 nm wavelength, region. We have demonstrated the ability to tune the power scattered and absorbed by varying the distance between the plasmonic layer and the reflector. Finite-difference-time-domain (FDTD) simulations demonstrate the tunability of the scattered and absorbed power with separation distance for a single Ag nanosphere near a planar Ag reflector. The tunability of the optical properties can be attributed to the modulation in the electric field driving the plasmonic resonance with separation distance. The simulation results indicate an intermediate distance where the scattered power peaks with minimal absorption losses. Random arrays of metal-islands were fabricated on varying thicknesses of a ZnO separation layer on a Ag reflector. Compared to a conventional textured Ag reflector, which has ?2% diffuse reflectance in the near-infrared spectral region, the fabricated plasmonic reflector with ?200 nm sized Ag metal islands at 100 nm separation distance from the Ag reflector shows a relatively higher, ?24%, integrated diffuse reflectance in the near bandgap, 600–1100 nm wavelength, region for thin film silicon solar cells
Influence of localized surface plasmon excitation in silver nanoparticles on the performance of silicon solar cells
No full textSilver nanoparticles have been fabricated on glass and silicon substrates, and silicon solar cells, by evaporation of 10 nm layers followed by thermal annealing. Distinct localized surface plasmon resonances are observed in the optical spectra of the annealed samples, and these strongly affect the cell reflectance and spectral response, both positively and negatively. At short wavelengths photocurrent is improved due to forward-scattering by quadrupolar modes, while at longer wavelengths photocurrent is deteriorated due to back-scattering by dipolar modes. Back-scattering is attributed to modification of the angular scattering distribution of the nanoparticles by the silicon substrate
Diffuse reflectance and absorption characterisation of a plasmonic back reflector for application in thin film Si solar cells
No full textSpectral tunability of plasmonic scattering by silver nanodiscs near a reflector
No full textThe scattering properties of a plasmonic array can be reinforced by placing the array near a planar reflector. Finite- Difference-Time-Domain (FDTD) simulations have been used to demonstrate the key design challenge of modulating the electric field that drives the plasmonic scattering, by varying the distance of a single Ag nanodisc from a Ag reflector. We show that the thickness of the dielectric separation layer plays a critical role in determining the spectral characteristics and the intensity of the power scattered by a Ag nanodisc near a reflector. A possible application of the designed structure as a plasmonic light-trap for thin Si solar cells is also experimentally demonstrated. Electron-beam lithography has been used to fabricate a pseudo-random array of 150nm plasmonic Ag nanodiscs on SiO2 on a Ag reflector substrate. The plasmonic reflector shows a high diffuse reflectance of ~54% in the near-infrared, near-bandgap 600-900nm wavelength region for thin Si solar cells, with a low broadband absorption loss of ~18%. Wavelength-angle resolved scattering measurements indicate an angular scattering range between 20° to 80° with maximum intensity of the scattered power in the 20° to 60° angular range
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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