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Challenge in Cu-rich CuInSe2 thin film solar cells: Defect caused by etching
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OPTICAL ANALYSIS OF EFFICIENCY LIMITATIONS OF CU(IN,GA)SE2 GROWN UNDER COPPER EXCESS
Full text linkSolar cells made from the compound semiconductor Cu(In,Ga)Se2 reach efficiencies of
22:9 % and are thus even better than multi crystalline silicon solar cells. All world records
are achieved using absorber layers with an overall copper deficient composition, but Cu-rich
grown samples have multiple favourable properties. However, especially losses in the open
circuit voltage limit the device performance. Within this work these efficiency limitations
of chalcopyrites grown with copper excess are investigated. The work has been divided
into four chapters addressing different scientific questions.
(i) Do alkali treatments improve Cu-rich absorber layers?
The alkali treatment, which lead to the recent improvements of the efficiency world record,
is adapted to CuInSe2 samples with Cu-rich composition. The treatment leads to an
improvement of the VOC which originates roughly equally from an improvement of the
bulk and the removal of a defect close to the interface. The treatment also improves the
VOC of Cu-poor samples. In both cases, the treatment increases the fill factor (FF) and
leads to a reduction of copper content at the surface.
(ii) Is the VOC limited by deep defects in Cu-rich Cu(In,Ga)Se2?
A deep defect, which likely limits the VOC, is observed in photoluminescence measurements
(PL) independent of a surface treatment. The defect level is proposed to originate from the
second charge transition of the CuIn antisite defect (CuIn(-1/-2)). During the investigation
also a peak at 0:9 eV is detected and attributed to a DA-transition involving a third
acceptor situated (135 ± 10) meV above the valence band. The A3 proposed to originate
from the indium vacancy (VIn). Furthermore the defect was detected in admittance
measurements and in Cu(In,Ga)Se2 samples with low gallium content.
(iii) Is the diode factor intrinsically higher in Cu-rich chalcopyrites?
Cu-rich solar cells exhibit larger diode ideality factors which reduce the FF. A direct link
between the power law exponent from intensity dependent PL measurements of absorbers
and the diode factor of devices is derived and verified using Cu-poor Cu(In,Ga)Se2 samples.
This optical diode factor is the same in Cu-rich and Cu-poor samples.
(iv) Is the quasi Fermi level splitting (qFLs) of Cu-rich Cu(In,Ga)Se2 absorber layers
comparable to Cu-poor samples?
Measuring the qFLs of passivated Cu-rich and Cu-poor Cu(In,Ga)Se2 samples, on average
a 120 meV lower splitting is determined for Cu-rich samples. This difference increases with
gallium content and is likely linked to a defect moving deeper into the bandgap, possibly
related to the second charge transition of the CuIn antisite defect.
Overall, samples with Cu-rich composition are not limited by the diode factor. However,
a deep defect band causes recombination lowering the qFLs and thus the VOC. This defect
is not removed by alkali treatments. A key component to improve Cu-rich solar cells in
the future, especially Cu(In,Ga)Se2, will be to remove or passivate this defect level.Curi-K and CuR
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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