1,720,964 research outputs found
Characterization by Confocal Laser Scanning Microscopy of the Phase Composition at Interfaces in Thick Films of Polymer Blends
Get PDFConfocal Laser Scanning Microscopy (CLSM) has been used as a fast, user-friendly, and noninvasive tool for characterizing
the phase composition differences at the substrate and air interfaces in thick films of polymer blends. A clearly different phase
composition at the blend/glass interface and at the blend/air interface has been detected. We show that PCBM preferentially
accumulates at the glass/blend interface, while P3HT preferentially accumulates at the blend/air interface, by comparing the
integrated signal intensity of the luminescence coming from both interfaces. Our results demonstrate that CLSM can be used
conveniently for the fast identification of a preferential phase segregation at interfaces in polymer blends. This is useful in the
research field on devices (like sensors or planar waveguides) that are based on very thick layers (thickness higher than 1 micron)
On the homogeneity of the external quantum efficiency in a free OPV roll-to-roll flexible solar module
No full textWe present a microscopic characterization of an organic photovoltaic (OPV) module demonstrator, fabricated within the “freeOPV” project. The local properties of the module are discussed on different length scales, from the submicrometric to the centimeters one, inferring the module structure and the origin of the different contributions to the optical and photoelectrical spatial inhomogeneity. We show that the local external quantum efficiency (EQE) in the individual cells of the module exhibits typical variations within 6–8% of the peak value over about 0.4 mm2. Larger variations are observed when comparing different cells across the module surface, with differences in the EQE peak values up to 1.6 times. Our results suggest that the roll-to-roll OPV module performance can be further improved by optimizing the printing uniformity as well as the charge extraction efficiency of electrodes
Study of the series resistance evolution in organic solar cells by use of the Lambert W function
No full textThe time evolution of the series resistance of bulk heterojunction solar cells realized and stored in inert atmosphere as well as in air has been monitored by fitting the experimental current vs. voltage characteristic to the analytical solution of the real diode equation obtained by means of the Lambert W function. The method allows to determine if and at what extent the standard one diode model can be used to acceptably describe the organic device in the field of a preliminary simple and fast evaluation of the series resistance evolution with time, without the need of complex and time consuming numerical fitting algorithms
Thickness dependence of the amplified spontaneous emission threshold and operational stability in poly(9,9-dioctylfluorene) active waveguides
Get PDFWe investigate the thickness dependence of the amplified spontaneous emission (ASE) threshold and operational lifetime in air-poly(9,9-dioctylfluorene)(PF8)-glass asymmetric active waveguides. We show that the ASE threshold decreases with the film thickness up to about 200 nm, and increases for higher thicknesses. The ASE operational lifetime increases with the thickness up to about 300 nm, and it is almost thickness independent for higher thickness. We show that the observed results are related to the guided mode confinement in the waveguide and to the spatial overlap between the guided modes and the excited region in the film
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
Study of spatial inhomogeneity in inverted all-polymer solar cells: Effect of solvent and annealing
No full textThe efficiency optimization of bulk heterojunction solar cells requires the control of the local active materials arrangement in order to obtain the best compromise between efficient charge generation and charge collection. Here, we investigate the large scale (10–100 μm) inhomogeneity of the photoluminescence (PL) and the external quantum efficiency (EQE) in inverted all-polymer solar cells (APSC) with regioregular poly(3-hexylthiophene) (P3HT):poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) active blends. The morphology and the local active polymer mixing are changed by depositing the active layer from four different solvents and by thermal annealing. The simultaneous PL and EQE mapping allowed us to inspect the effects of local irregularities of active layer thickness, polymer mixing, polymer aggregation on the charge generation and collection efficiencies. In particular, we show that the increase of the solvent boiling point affects the EQE non-uniformity due to thickness fluctuations, the density non-uniformity of rrP3HT aggregate phase, and the blend components clustering. The thermal annealing leads to a general improvement of EQE and to an F8BT clustering in all the samples with locally decrease of the EQE. We estimate that the film uniformity optimization can lead to a total EQE improvement between 2.7 and 6.3 times
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
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