1,720,982 research outputs found
Mapping quality and parameters of photovoltaic liquid crystal modulators
No full textPhotovoltaic light modulators integrate liquid crystals and solar cells and offer an exciting prospect for autonomous, smart displays and visors. Illumination produces a photovoltage that modifies the liquid crystal alignment and light transmission. However, determining their properties, for example, the voltage dropped across the liquid crystal, different pretilts or anchoring energies, inherent to asymmetric cell designs, poses significant challenges. We have successfully applied to such photovoltaic modulators a new measurement methodology based on wide-area cross-polarized intensity measurements, coupled to an Ericksen-Leslie model. We have implemented it in a versatile optical analyzer, driven by a Matlab graphical user interface
Novel low bandgap phenothiazine functionalized DPP derivatives prepared by direct heteroarylation: Application in bulk heterojunction organic solar cells
No full textThe synthesis by direct heteroarylation of three novel low bandgap donor-acceptor-donor molecules is reported herein. The molecules are based on three different diketopyrrolo-pyrrole (DPP) electron deficient cores, functionalized with different electron rich heteroarenes, (thiophene, thiazole and thienothiophene) and symmetrically linked to two terminal donor phenothiazine rings. The optical properties of the synthesized dyes have been measured both in solution and as thin film and a focus has been given on the study of optoelectronic properties as a function of the different heteroarenes (thiophene, thiazole or thienothiophene) functionalizing the DPP core. Bandgap values as small as 1.55 eV have been observed. The energy of the Frontier orbitals has been estimated by means of electrochemical characterization. The electronic properties of the reported molecules have been investigated more in details by computational analysis performed at the DFT level. The new dyes were used as donor materials in BHJ solar cells and the photovoltaic characterization of these devices led to a maximum power conversion efficiency of 0.7%
Study of charge transport in low band-gap semiconducting polymers and its impact on phototovoltaic performances
No full textLe transport de charges dans une série de copolymères à faible bande interdite basés sur l'alternance de motifs riches en électrons (thiophène, thiénothiophène) et d‘unités déficients en électrons (benzothiadiazole) et dans leurs mélanges avec un dérivé du fullerène (PCBM-C60) a été étudié. Les polymères sont différenciés par la structure moléculaire de leur coeur conjugué et par la nature, la position et la densité de leurs chaines latérales. Dans les polymères purs, la mobilité a été étudiée en fonction de la densité de charges par le biais de l’analyses de caractéristiques électriques de transistors à effet de champ et de dispositifs à un seul type de porteurs dont le courant est limité par la charge d’espace. En utilisant le modèle de transport de charges développé par Vissenberg et al., nous avons pu estimer le degré de désordre dans le film organique et corréler le transport de charge avec le degré d’ordre structural mesuré par la diffraction des Rayons-X. Ces polymères ont été conçus pour être utilisés dans la couche active des cellules solaires organiques. Grâce à l’étude du transport de charges dans les mélanges à différents ratios massiques polymères:fullerène, nous avons mis en évidence l’effet considérable de la structure moléculaire sur le ratio optimal polymère:fullerène. Aussi, nous avons pu montrer que la nature des chaînes latérales joue un rôle important dans l’obtention d’un chemin de percolation optimal à la conduction des électrons.The charge transport in a series of low band-gap copolymers based on the alternation of electron-rich units (thiophene, thienothiophene) and electron-deficient units (benzothiadiazole) and in their blends with a fullerene derivative (PCBM-C60) is investigated. The polymers are differentiated by the molecular structure of the conjugated backbone and by the nature, position and density of alkyl side chains. In pristine polymer films, the hole mobility has been investigated as a function of charge carrier density by analyzing the electrical response of field-effect transistors and single carrier spacecharge- limited current devices. By using the charge transport model developed by Vissenberg et al., we could quantify the structural disorder for the different polymers and correlate their degree of anisotropy with structural data obtained by Grazing Incidence Wide Angle X-ray diffraction. These polymers have been used in the active layer of organic solar cells. The ambipolar chargetransport was investigated in the corresponding polymer:fullerene blends. The results show that the side chains play a major role on the polymer: fullerene interactions and controls the optimal weight ratio. Also, we have shown that the nature of the side chains has a strong impact in the optimal electron conducting pathways
Etude du transport de charges dans les polymères semi-conducteurs à faible bande interdite et de son impact sur les performances photovoltaïques
No full textThe charge transport in a series of low band-gap copolymers based on the alternation of electron-rich units (thiophene, thienothiophene) and electron-deficient units (benzothiadiazole) and in their blends with a fullerene derivative (PCBM-C60) is investigated. The polymers are differentiated by the molecular structure of the conjugated backbone and by the nature, position and density of alkyl side chains. In pristine polymer films, the hole mobility has been investigated as a function of charge carrier density by analyzing the electrical response of field-effect transistors and single carrier spacecharge- limited current devices. By using the charge transport model developed by Vissenberg et al., we could quantify the structural disorder for the different polymers and correlate their degree of anisotropy with structural data obtained by Grazing Incidence Wide Angle X-ray diffraction. These polymers have been used in the active layer of organic solar cells. The ambipolar chargetransport was investigated in the corresponding polymer:fullerene blends. The results show that the side chains play a major role on the polymer: fullerene interactions and controls the optimal weight ratio. Also, we have shown that the nature of the side chains has a strong impact in the optimal electron conducting pathways.Le transport de charges dans une série de copolymères à faible bande interdite basés sur l'alternance de motifs riches en électrons (thiophène, thiénothiophène) et d‘unités déficients en électrons (benzothiadiazole) et dans leurs mélanges avec un dérivé du fullerène (PCBM-C60) a été étudié. Les polymères sont différenciés par la structure moléculaire de leur coeur conjugué et par la nature, la position et la densité de leurs chaines latérales. Dans les polymères purs, la mobilité a été étudiée en fonction de la densité de charges par le biais de l’analyses de caractéristiques électriques de transistors à effet de champ et de dispositifs à un seul type de porteurs dont le courant est limité par la charge d’espace. En utilisant le modèle de transport de charges développé par Vissenberg et al., nous avons pu estimer le degré de désordre dans le film organique et corréler le transport de charge avec le degré d’ordre structural mesuré par la diffraction des Rayons-X. Ces polymères ont été conçus pour être utilisés dans la couche active des cellules solaires organiques. Grâce à l’étude du transport de charges dans les mélanges à différents ratios massiques polymères:fullerène, nous avons mis en évidence l’effet considérable de la structure moléculaire sur le ratio optimal polymère:fullerène. Aussi, nous avons pu montrer que la nature des chaînes latérales joue un rôle important dans l’obtention d’un chemin de percolation optimal à la conduction des électrons
Etude du transport de charges dans les polymères semi-conducteurs à faible bande interdite et de son impact sur les performances photovoltaïques
No full textThe charge transport in a series of low band-gap copolymers based on the alternation of electron-rich units (thiophene, thienothiophene) and electron-deficient units (benzothiadiazole) and in their blends with a fullerene derivative (PCBM-C60) is investigated. The polymers are differentiated by the molecular structure of the conjugated backbone and by the nature, position and density of alkyl side chains. In pristine polymer films, the hole mobility has been investigated as a function of charge carrier density by analyzing the electrical response of field-effect transistors and single carrier spacecharge- limited current devices. By using the charge transport model developed by Vissenberg et al., we could quantify the structural disorder for the different polymers and correlate their degree of anisotropy with structural data obtained by Grazing Incidence Wide Angle X-ray diffraction. These polymers have been used in the active layer of organic solar cells. The ambipolar chargetransport was investigated in the corresponding polymer:fullerene blends. The results show that the side chains play a major role on the polymer: fullerene interactions and controls the optimal weight ratio. Also, we have shown that the nature of the side chains has a strong impact in the optimal electron conducting pathways.Le transport de charges dans une série de copolymères à faible bande interdite basés sur l'alternance de motifs riches en électrons (thiophène, thiénothiophène) et d‘unités déficients en électrons (benzothiadiazole) et dans leurs mélanges avec un dérivé du fullerène (PCBM-C60) a été étudié. Les polymères sont différenciés par la structure moléculaire de leur coeur conjugué et par la nature, la position et la densité de leurs chaines latérales. Dans les polymères purs, la mobilité a été étudiée en fonction de la densité de charges par le biais de l’analyses de caractéristiques électriques de transistors à effet de champ et de dispositifs à un seul type de porteurs dont le courant est limité par la charge d’espace. En utilisant le modèle de transport de charges développé par Vissenberg et al., nous avons pu estimer le degré de désordre dans le film organique et corréler le transport de charge avec le degré d’ordre structural mesuré par la diffraction des Rayons-X. Ces polymères ont été conçus pour être utilisés dans la couche active des cellules solaires organiques. Grâce à l’étude du transport de charges dans les mélanges à différents ratios massiques polymères:fullerène, nous avons mis en évidence l’effet considérable de la structure moléculaire sur le ratio optimal polymère:fullerène. Aussi, nous avons pu montrer que la nature des chaînes latérales joue un rôle important dans l’obtention d’un chemin de percolation optimal à la conduction des électrons
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
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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