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Untersuchung von hybriden organisch-anorganischen Blei-Halogenid-Perowskiten mittels modulierter Oberflächenphotospannungsspektroskopie
No full textHybrid organic-inorganic metal halide perovskites (called here perovskites) have emerged as a new group of materials for highly efficient solar cells (SCs) based on earth abundant elements which can be processed from solutions at low temperature. CH3NH3Pb(I1-xBrx)3 perovskite films were studied in the thesis since it belongs to the materials which are of great interest for top SCs in tandem SCs with c-Si bottom SCs due to its tunable band gap. Electronic properties of CH3NH3Pb(I1-xBrx)3 perovskite films sensitively depend on crystallization and defect formation and are crucial for the performance and stability of SCs. The band gap (Eg), exponential tail states (Et) and the diffusion length (L) are decisive parameters for absorbers in SCs since they give principle limitations for photo-generation and Fermi-level splitting. In CH3NH3Pb(I1-xBrx)3 perovskites, Eg, Et and L are not necessarily constant and can depend, for example, on the preparation conditions and degradation. Therefore, Eg, Et and L of CH3NH3Pb(I1-xBrx)3 perovskites were studied with respect to stoichiometry, interfaces, degradation and temperature. Modulated surface photovoltage (SPV) spectroscopy was used as the main characterization technique. Modulated SPV spectroscopy allows for the contactless and very sensitive characterization of Eg, Et, direction of charge separation and L (after Goodman) without the requirement of the preparation of contacts after or during different stages of layer preparation, light soaking etc. Vegard’s law was applied to obtain the composition of CH3NH3Pb(I1-xBrx)3 films. The Eg of CH3NH3Pb(I1-xBrx)3 films varied between 1.59 eV to 2.30 eV depending on the stoichiometry whereas the bowing parameter was 0.36 eV. The influence of the substrate on Eg and Et of CH3NH3PbI3 films was investigated. It has been found, for example, that Eg and Et of CH3NH3PbBr3 sensitively depend on the substrate and on soaking in nitrogen atmosphere and that light soaking has strong influence on the direction of modulated charge separation. CH3NH3PbI3 deposited on double layers of TiO2-PCBM and SnO2-PCBM showed a constant band gap of 1.58 eV and a low scatter in Et. This was attributed to the modification of the TiO2 or SnO2/CH3NH3PbI3 interfaces by PCBM allowing for efficient charge separation and transfer and well reproducible conditions for the layer formation. A decrease of L with light soaking was observed and can be attributed to light induced degradation due to charging and discharging of trap states and formation of defects at the TiO2/ CH3NH3PbI3 interface. Furthermore, Eg and Et of CH3NH3PbI3 stabilized with PMMA increased with increasing temperature, i.e. thermal expansion gives the predominant contribution to the temperature dependence of Eg of CH3NH3PbI3 whereas dynamic disorder was limited by phonons. A jump-like increase of Eg in the region of phase transition was attributed to the phase transition from the tetragonal to the cubic phases.Hybride organisch-anorganische Metallhalidperovskite (hier kurz Perovskite genannt) sind eine neue Materialgruppe für hocheffiziente Solarzellen, welche auf in der Erdkruste reich verfügbaren Elementen basieren und welche bei niedrigen Temperaturen aus Lösungen hergestellt werden können. Perovskitschichten aus CH3NH3Pb(I1-xBrx)3 wurden in der Doktorarbeit untersucht, da diese für Anwendungen als Topzellen in Tandemsolarzellen mit c-Si-Bottomzellen aufgrund der einstellbaren Bandlücke von großem Interesse sind. Die elektronischen Eigenschaften von Perovskitschichten aus CH3NH3Pb(I1-xBrx)3 hängen empfindlich von der Kristallisation und der Bildung von Defekten ab und sind kritisch für die Leistung und Stabilität von Solarzellen. Die Bandlücke (Eg), die exponentiellen Bandausläufer (Et) und die Diffusionslänge (L) sind entscheidend für Absorber in Solarzellen, da sie die Photogeneration und die Aufspaltung der Fermi-Niveaus limitieren. Eg, Et und L sind in Perovskitschichten aus CH3NH3Pb(I1-xBrx)3 nicht zwingend konstant und hängen z.B von der Präparation und der Degradierung ab. Deshalb wurden Eg, Et und L mit Hinblick auf die Stöchiometrie, Grenzflächen, Degradierung und Temperatur untersucht. Als Hauptuntersuchungsmethode wurde die modulierte Oberflächenphotospannungs-spektroskopie (SPV) eingesetzt. Die SPV erlaubt eine kontaktlose und außerordentlich empfindliche Bestimmung von Eg, Et, Richtung der Ladungstrennung und L (nach Goodman) nach oder während verschiedener Schritte der Präparation oder Degradierung, z.B. unter Beleuchtung. Anhand des Vegard’schen Gesetzes wurde die Stöchiometrie von CH3NH3Pb(I1-xBrx)3 ermittelt. Eg von CH3NH3Pb(I1-xBrx)3 variierte zwischen 1.59 und 2.30 eV, wobei der Bowingparameter 0.36 eV betrug. Starke Einflüsse des Substrates und der Lagerung in Stickstoffatmosphäre auf Eg, Et und die Richtung der modulierten Ladungstrennung wurden u.a. in CH3NH3PbBr3 festgestellt. Eg betrug für auf TiO2/PCBM oder SnO2/PCBM abgeschiedenes CH3NH3PbI3 1.58 eV und Et zeigte nur geringfügige Variationen, PCBM hat also kaum Einfluss auf Eg und Et. und trägt sehr zur effizienten Ladungstrennung und zur gut reproduzierbaren Herstellung von Perovskitschichten bei. Die beobachtete Abnahme von L in CH3NH3PbI3 unter Beleuchtung kann der Umladung von Defekten sowie der Generation zusätzlicher Defekte besonders im Bereich der Grenzfläche zwischen TiO2 und CH3NH3PbI3 zugeordnet werden. Eg und Et stiegen mit steigender Temperatur für mit PMMA stabilisiertes CH3NH3PbI3 an, was auf den dominanten Einfluss der thermischen Ausdehnung und der Limitierung der dynamischen Unordnung durch Phononen zurückzuführen ist. Ein sprunghafter Anstieg von Eg bei etwas höheren Temperaturen wurde dem Übergang der tetragonalen Phase von CH3NH3PbI3 in die kubische Phase von CH3NH3PbI3 zugeordnet
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
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
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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