1,720,952 research outputs found
Intermediate scale bandgap fluctuations in ultrathin Cu(In,Ga)Se2 absorber layers
No full textUltrathin single- and three-stage Cu(In,Ga)Se-2 absorber layers were analyzed with room temperature photoluminescence (PL) spectra. An anomalous blueshift was observed upon increasing carrier injection for both samples. This blueshift was attributed to the presence of bandgap fluctuations that are of the same order as the minority carrier diffusion length. From time resolved measurements, a diffusion length of a few 100nms was deduced. The single-stage spectrum consists of two peaks, and the sample was, therefore, also analyzed by hyperspectral imaging, providing lateral PL and reflectance data with 1 mu m resolution. Marginal variations were observed in the PL yield and spectra. This homogeneity could again be attributed to an intermediate scale of the bandgap fluctuation with an upper limit of 1 mu m for the scale of the lateral bandgap fluctuations. The two peaks in the PL spectra of the single-stage sample could be attributed to interference, and correction methods were applied. The bandgap fluctuations were extracted for the three-stage and single-stage sample and were 45meV and 72 +/- 3meV, respectively. It is suggested that this difference is attributed to the smaller grains and larger amount of grain boundaries in the single-stage sample.This work received funding from the European Union's H2020 Research and Innovation Program under Grant Agreement No. 715027. We acknowledge Photon etc. and Professor Delphine Bouilly's research group from IRIC for the hyperspectral measurements and Erik Spaans for the python program
Impact of photovoltaic technology and feeder voltage level on the efficiency of façade building-integrated photovoltaic systems
No full textsponsorship: This project receives the support of the European Union, the European Regional Development Fund ERDF, Flanders Innovation & Entrepreneurship and the Province of Limburg. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 751159. Special thanks goes to C. Sheehan from Bourns for providing the required inductor specifications. Patrizio Manganiello was previously with IMEC, Kapeldreef 75, Leuven, Belgium. (European Union, European Regional Development Fund ERDF, Flanders Innovation & Entrepreneurship, Province of Limburg, European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie|751159, Marie Curie Actions (MSCA)|751159)status: Published onlin
A study of the degradation mechanisms of ultra-thin CIGS solar cells submitted to a damp heat environment
No full textProducing the green energy of tomorrow will require highly efficient as well as energy-, and cost-effective solar cells in addition to having reasonable lifetimes. To determine if CIGS can be made to submit to these constraints, we produced ultra-thin (500nm) single-stage coevaporated CIGS solar cells. We doped these cells with varying amounts and types of alkali atoms and submitted them to accelerated lifetime testing. Results showed definite effect of the alkali concentration on the degradation of the cells but showed limited migration. Instead, the seeping of water into the grain boundaries was identified as the main culprit for performance degradation.This work received funding from the European Union's H2020 research and innovation program under grant agreement No. 715027Kohl, T (corresponding author), Hasselt Univ Partner Solliance, Inst Mat Res IMO, Agoralaan Gebouw H, B-3590 Diepenbeek, Belgium ; Imec Div IMOMEC Partner Solliance, Wetenschapspk 1, B-3590 Diepenbeek, Belgium ; EnergyVille, Thorpk, B-8310 Poort Genk, Belgium
A study of the degradation mechanisms of ultra-thin CIGS solar cells submitted to a damp heat environment
No full textProducing the green energy of tomorrow will require highly efficient as well as energy-, and cost-effective solar cells in addition to having reasonable lifetimes. To determine if CIGS can be made to submit to these constraints, we produced ultra-thin (500nm) single-stage coevaporated CIGS solar cells. We doped these cells with varying amounts and types of alkali atoms and submitted them to accelerated lifetime testing. Results showed definite effect of the alkali concentration on the degradation of the cells but showed limited migration. Instead, the seeping of water into the grain boundaries was identified as the main culprit for performance degradation.This work received funding from the European Union's H2020 research and innovation program under grant agreement No. 715027Kohl, T (corresponding author), Hasselt Univ Partner Solliance, Inst Mat Res IMO, Agoralaan Gebouw H, B-3590 Diepenbeek, Belgium ; Imec Div IMOMEC Partner Solliance, Wetenschapspk 1, B-3590 Diepenbeek, Belgium ; EnergyVille, Thorpk, B-8310 Poort Genk, Belgium
with Different Cu/(Ga + In) Ratios
No full textIn ultrathin Cu(In,Ga)Se-2(CIGS) film solar cells, the CdS/CIGS interface may become one of the limiting factors for efficiency. The first step toward reducing the impact of this problem could be a surface treatment process to improve the quality of the front interface. The purpose of this study is to have a better understanding of the effect of wet chemical surface treatment, using ammonium sulfide ((NH4)(2)S), on CIGS thin film layers with different Cu/(Ga + In) (CGI) ratios. Herein, photoluminescence (PL) and time-resolved PL (TRPL) studies are conducted on bare CIGS, ammonium sulfide-treated CIGS thin films, and samples with CdS. In bare CIGS, CGI ratio-dependent changes in PL are observed on both a low-energy (defect related transition) and a high-energy peak (band-to-band transition). After the surface treatment, the PL maximum increases by factors ranging from 4 to 11 depending on the CGI ratio, accompanied by a slower decay. Trends with similar improvement as in the PL study are observed in the performance of the solar cells. It is shown that the impact of the surface treatment is beneficial independently of the CGI ratio of the absorber layers. In all cases, the treatment is shown to improve the efficiency.This work received funding from the European Union's H2020 research and innovation program under grant agreement No. 715027.Buldu, DG (corresponding author), Hasselt Univ Partner Solliance, Inst Mat Res IMO, Agoralaan Gebouw H, B-3590 Diepenbeek, Belgium ; Imec Div IMOMEC Partner Solliance, Wetenschapspk 1, B-3590 Diepenbeek, Belgium ; EnergyVille, Thorpk,Poort Genk 8310 & 8320, B-3600 Genk, Belgium.
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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
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