1,721,125 research outputs found
Improving solar cell performance through surface modification of silicon
No full textThis project sets out to improve the efficiency of thin crystalline silicon solar cells by enhancing the photoexcitation through light harvesting, and by developing a novel surface passivation technique via the covalent attachment of organic molecules to the surface. To aid the characterisation of these novel structures, we have developed a new measurement technique for surface recombination using the Kelvin prove.A passivation method through the attachment of alkyl monolayers to the silicon surface has been developed. These layers were shown to have good passivation properties whilst retaining excellent resilience to oxidation. The passivation effect was determined to be caused by the generation of surface charge, as measured by the Kelvin probe. Further functionalisation of the organic monolayers was undertaken to attach fluorescent chromophores. A novel method for measurement of the surface recombination velocity was developed utilising the Kelvin probe. Changing the incident photon flux, and thus the photogenerated current, allows measurement of the surface recombination current through the change in surface photovoltage. This dependence can then be used to extract the value of the surface recombination velocity. Furthermore, we have shown that this method can be developed further into a mapping technique for surface recombination lifetime, of potentially significant industrial interest.The effect of the silicon surface charge on the passivation observed has been investigated through the attachment of charged monolayers. It was found that through the attachment of a positive charge, the observed recombination lifetime in n-type silicon decreased whilst a negative charge (through the attachment of carboxylic acid groups to the surface) was found to improve the surface passivation. The carboxylic acid functional groups were charged through immersion in triethylamine (base) and returned to the neutral, starting state through immersion in acetic acid. We have found that the recombination lifetime decreases linearly with decreasing charge-surface distance. This technique allows an in-depth study of surface passivation to be carried out by separating the two principal causes for passivation – the removal of surface states and charge attachment to the surface.Fluorescent chromophores were attached to the silicon surface by two different techniques – through the reaction of an alcohol-terminated monolayer with an acyl chloride porphyrin and by palladium-catalysed cross-coupling of an allyl-terminated surface with a cyanine dye. The fluorescence quenching was investigated at various chromophore-silicon distances by varying the length of the alkyl chain spacer. We find that the fluorescence lifetime decreases with decreasing chromophore-silicon distance, and follows a logarithmic trend. Further work is required, however, to combine sensitisation with surface passivation as incorporation of a sensitisation layer by the palladium cross coupling of an allyl-terminated surface results in metal contamination to the surface, reducing recombination lifetime
Harvesting sunshine: solar cells, photosynthesis and the thermodynamics of light
No full textEffective capture of sunlight represents one of the grand challenges of photovoltaics today. This paper looks at the opportunities that exist, at the fundamental level, to manage light as the first step of photovoltaic conversion; in particular, how photonics can improve the efficiency and reduce the cost of solar cells. Starting from the current view of light trapping we shall introduce an additional variable: photon frequency. The example of fluorescent collectors will be used to discuss the principal features of frequency management, leading to a novel form of light trapping and, ultimately, the photonic bandgap solar cell. The discussion will be guided by arguments based on thermodynamics to describe photon transformation as part of the absorption / emission / conversion process. By drawing parallels with the capture of light in photosynthetic organisms we shall briefly discuss another important aspect: light harvesting energy collection, and the oportunity this represents for reducing the materials usage in future generations of solar cell
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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