1,720,975 research outputs found
Replication Data for: Hot Carrier Extraction in CH3NH3PbI3 Unveiled by Pump-Push-Probe Spectroscopy
No full textHalide perovskites recently emerged as a promising material for development in hot carrier solar cells (HCSCs), where the excess energy of above-bandgap photons is harvested before being wasted to heat to enhance device efficiency. Presently, HC separation and transfer processes at higher energy states remain poorly understood. Herein, we investigate the excited-state dynamics in the ubiquitous CH3NH3PbI3 using pump-push-probe spectroscopy, which has its intrinsic advantages for studying these dynamics over the conventional transient spectroscopy, albeit complementary to one another. By exploiting the broad excited state absorption characteristics, our findings reveal the transfer of HCs from these higher energy states into bathophenanthroline (bphen), an energy selective organic acceptor far above perovskite's bandedges. Complete HC extraction is realized only after overcoming the interfacial barrier formed at the heterojunction, estimated to be between 1.01 eV and 1.08 eV above bphen’s lowest unoccupied molecular orbital level. The insights gained from this study are essential for the development of a new class of optoelectronics
Engineering carrier dynamics in lead halide perovskites
No full textOrganic-inorganic hybrid perovskites have attracted immense attention primarily due to its outstanding photovoltaic and light emission properties. Specifically, certified power conversion efficiencies exceeding 20 % have been demonstrated in perovskite solar cells – attributed to their large absorption coefficients and long, balanced, ambipolar diffusion lengths, large grains and its unique defect tolerance. Careful morphological control is needed to form dense, uniform films essential for high performance devices. However, the resultant fundamental optoelectronic properties of such process controls are not well understood. In addition, the higher excited states that can aid in breaking the detailed balance limit is also unexplored. This thesis reports on a series of studies using ultrafast optical spectroscopy on the archetypal bulk 3D perovskite, MAPI, to provide insights on the photophysics and recombination dynamics of this class of materials. Here, process controls in fabricating perovskite thin films refers to treatments to the film, in the form of solvent engineering and additives, and to the substrate for hydrophilicity. Our findings reveal that solvent engineering of MAPI, i.e., dripping of toluene during spincoating which is key to improving film morphologies and subsequent solar cell efficiencies, had resulted in increased trap densities. We attribute this anomalous behaviour to an interplay of factors where the improved film morphology had also resulted in the lengthening of the carrier recombination lifetimes. Interestingly, depending on the combination of treatments, the charge extraction interface can go from injecting to non-injecting. Exceptionally low carrier recombination rates in lead halide perovskites is crucial for its high performance. By careful optimisation of the additive concentration, improvements to device performance were observed when H2O was added to MAPI as an additive. Trace amounts of H2O passivates the trap states leading to reduced recombination rates, markedly improved carrier lifetimes and Jsc. At the optimal additive concentration of 1 vol% H2O, higher order carrier recombination is suppressed, and the greatly reduced monomolecular and bimolecular recombination rates was correlated with an increase in power conversion efficiencies. Process controls have all but ensured the unprecedented growth in record efficiencies of perovskite solar cells. However, it slows as it approaches the detailed balance limit of solar cells. One way to surpass this limit is to exploit the concept of hot carriers -- photoexcited carriers in higher excited states. A technique to directly probe these states is presented, and through this, the broad photoinduced absorption band was revealed to be attributed to the promotion of photoexcited carriers to higher energy states. However, the observed sub-picosecond thermalisation times of these higher excited states may prove difficult for hot carrier extraction. Importantly, our results underscores the importance of judiciously choosing process controls to optimise optoelectronic properties of perovskite devices.Doctor of Philosoph
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
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