1,720,983 research outputs found
Experimental demonstration of mid-IR absorption enhancement in single layer CVD graphene
No full textMid-IR absorption of single layer graphene (SLG) was simulated and experimentally demonstrated by embedding a SLG grown by chemical vapor deposition (CVD) inside a Fabry- Perot (FP) filter made by alternating quarter wave Si and SiO2 layers fabricated by radiofrequency sputtering. The absorption from the graphene layer was modeled by using COMSOL Multiphysics in four different configurations, depending on its position inside the filter, an asymmetric FP made of two different dielectric mirrors separated by a cavity. In the first three configurations, graphene was inserted at the center of the optical cavity and inside the top or bottom dielectric mirror forming the FP. The fourth configuration involves two layers of graphene, each positioned inside one of the dielectric mirrors. The calculated electric field distribution inside the FP shows two symmetric maxima just above and below the cavity, i.e., inside the mirrors, while the electric field at the center of the cavity is negligible. For the experimental demonstration, the graphene geometry corresponding to the maximum electric field intensity was chosen, and, between two equivalent alternatives, the one with the easiest fabrication procedure was selected. Results demonstrate a maximum experimental absorption of 50% at 4342 nm for SLG when inserted in the top mirror of the FP, in excellent agreement with the simulated value of 53%
Hydrogen plasma and thermal annealing treatments on a-Si:H thin film for c-Si surface passivation
No full textHigh efficiency solar cells can be fruitfully built using the amorphous/crystalline silicon technology, taking advantage of the high Voc that occurs as a consequence of excellent c-Si surface passivation provided by a-Si:H films. Improvements of the interface quality can be obtained using post deposition treatments such as hydrogen plasma and thermal annealing. We propose the use of surface photovoltage technique, as a contact-less tool to evaluate the energetic distribution of the state density at amorphous/crystalline silicon interface, and FTIR spectroscopy of the same samples to appreciate the evolution of Si-H and Si- H2 bonds. This approach leads to interesting applications for monitoring and improving the interface electronic quality, which is extremely susceptible to the different treatments adopted. We found that thermal annealing produces a metastable state which goes back to the initial state after just 48 hours, while the effect of hydrogen plasma post-treatment results more stable. Moreover H2 plasma reduces the defect density of one order of magnitude with respect to thermal annealing and keeps it constant also after one month. The hydrogen plasma is able to reduce the defect density but at the same time increases the surface charge within the a-Si:H film due to the H+ ions accumulated during the plasma exposure, leading to a more stable configuration
Cu2SnS3 based solar cell with 3% efficiency
No full textCu2SnS3 is an earth abundant material suitable for photovoltaic applications. Unfortunately, the material still suffers of a low diffusion length of the carriers due to the presence of spurious phases, voids, defects and small grain size. In order to improve the quality of our samples, the influence of the deposition parameters on its structural properties has been studied. The solar cell obtained with the optimized Cu2SnS3 has shown an external quantum yield larger than 80% around 500 nm a conversion efficiency in the order of 3%, a Jsc of 26 mA and a Voc of 240 mV, one of the world best result obtained with a Cu2SnS3 based solar cell. Furthermore the external quantum yield at wavelength larger than 1200 nm is still around 30% making this material interesting for IR detectors also. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Laser Treatment to form An Effective Base Contact in a - Si:H/c-Si Heterojunction Solar Cells
No full textIn this paper we investigate the p-type a-Si:H/ia-Si:H/p-type c-Si structure, commonly used as base contact in amorphous/crystalline silicon heterojunction solar cell when fabricated on p-type c-Si wafer. Even though the most effective amorphous silicon/crystalline silicon heterostructure is based on n-type c-Si due to higher bulk lifetime, the p-type c-Si still remains the most common and cheaper substrate for silicon based solar cell. In particular we study the effect of localized 532 nm pulsed laser treatment at different laser conditions in order to reduce the cell series resistance due to the base contact. In this approach the p-type a-Si:H layer is used as a source of boron dopant. Depending on the thickness of the p-type a-Si:H film, when the laser beam is focused on p-type a-Si:H layer the boron can be transferred into the c-Si base to form an overdoped region and then an effective local Back Surface Field, able to enhance the hole collection at the metal of the base electrode in the p-type c-Si based heterojunction solar cell. The application of a thin Aluminum layer on top of the amorphous silicon to be treated by laser is also concerned. Series resistance of a transverse structure composed by the laser treated p-type a-Si:H/c-Si/opposite surface contacted by InGa is considered to optimize the laser procedure. Values as low as 0.5 Ωcm2 are obtained when the aluminum layer is adopted. © 2015 The Authors
Effect of Hydrogen Gas Dilution on Sputtered Al:ZnO Film
No full textAbstractAl doped zinc oxide (ZnO:Al) is a transparent and conductive oxide used as contact and antireflection layer in solar cell based on Si or chalcogenide. Generally it is grown by magnetron sputtering but the resistivity of our films grown with this technique are still in the order of 10-3Ωcm for layers grown at the temperatures used to produce the solar cells. The doping property of Hydrogen for Al:ZnO grown with two different sputtering techniques, DC magnetron sputtering and Pulsed magnetron sputtering at different growth parameters have been studied and the sample characterized optically, electrically and structurally. The best resistivity is 6.7*10-4Ωcm was obtained using Pulsed magnetron sputtering
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
- …
