1,720,954 research outputs found
Effect of a 2D-Modification of Cs2AgBiBr6 on Nucleation and Contact Formation of Subsequently Deposited Hole Transport Layers as Revealed by In Situ Growth Studies
Full text link: A two-dimensional (2D) perovskite interlayer prepared by modification of a three-dimensional (3D) perovskite absorber with organic ammonium ions such as butylammonium (BA+) or phenethylammonium (PEA+) between the 3D perovskite and contact layers is widely known to significantly improve the performance of perovskite solar cells. This has also been confirmed previously for the lead-free double perovskite absorber Cs2AgBiBr6. In this work, film growth of copper phthalocyanine (CuPc) or pentacene (Pn), used as model hole transport materials (HTM), was investigated. Mimicking solar cell geometry, the HTMs were evaporated onto thin films of 2D perovskites BA4AgBiBr8 or PEA4AgBiBr8, as well as on 3D Cs2AgBiBr6, either in its pristine form or after modification by BA+ or PEA+. The morphology and work function were inspected intermittently with respect to the evaporation of the HTMs by Kelvin probe force microscopy at different average film thicknesses. By these means, the origin of device improvements following a 2D-modification in contact with HTMs, as established earlier, was revealed by analyzing in detail the interface of the HTM with the respective perovskite starting at monolayer coverage and proceeding toward bulk thickness. On modified Cs2AgBiBr6, the energy alignment between the perovskite and the HTM was found to be well confined, and the growth of both HTMs was improved compared to pristine Cs2AgBiBr6. HTM growth occurred more homogeneously and led to layer formation, even at early stages of deposition. For CuPc as HTM, these changes were accompanied by preferential formation of needles in a crystal phase different from that formed on pristine Cs2AgBiBr6, as also detected on 2D PEA4AgBiBr8. Pn formed large dendritic islands on the 2D perovskites as well as on layered terraces formed upon ammonium modification of Cs2AgBiBr6, in contrast to the growth of small grains on pristine Cs2AgBiBr6. Implications of these observed changes in film growth and energy level alignment on the observed contact characteristics with the HTMs in model solar cells are discussed. Insight into the mechanism of improving perovskite-based devices by use of 2D/3D perovskite heterostructures is, thereby, provided by these measurements using CuPc or Pn as model HTMs
Transformation of Polarization Mechanisms by Dimensional Reduction in Lead-Free Silver Bismuth Bromide Double-Perovskite Thin Films
No full textLead-freehalideperovskitematerialsarediscussedasalternativematerialsto replacelead-containingperovskitesandminimizerisksto humanhealthandthe environment.Dimensionalreductionof theoctahedralmetalhalidenetworkby incorporatinglargerorganiccationsincludingphenethylammonium(PEA)representsan attractiveoppor-tunityto tailortheirpropertiestowardapplications.Here,differencesincharacteristicsunderan appliedconstantvoltageare detected,whicharisefromthe dimensionalreductionof the Cs2AgBiBr6double-perovskiteto(PEA)4AgBiBr8. Thinfilmsconsistingof thesecompoundswerespin-coatedontomicrostructuredinterdigitatedelectrodearrays.Current−voltageandKelvinprobeforcemicroscopymeasurementswereperformedto revealthe overallor locallyresolvedconsequencesof an appliedelectricfield.Bothmaterialsshoweda reversibleion displacementin smallelectricfields.At higherfieldstrengths,however,Cs2AgBiBr6exhibiteda persistentcontactmodificationat the interfaceof the perovskiteandthecontactmetaldueto migratingions,whereas(PEA)4AgBiBr8stillshoweda reversibleseparationof ions.Insulatinginterlayersthatwidelyattenuatethe currentdemonstratethattheseeffectsare inducedby electricfieldsonly,independentof chargeinjection.Theobtainedresultsprovidean explanationof improvementsof perovskitecontactsby interfacialengineering,inparticular,describinghowa two-dimensional(2D)perovskitelayerreducesthe hysteresisandinterfacialresistancein contactto athree-dimensional(3D)double-perovskit
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
- …
