1,720,957 research outputs found
CZTS-based photovoltaic devices by non-vacuum techniques
Full text linkThe primary benefit of thin-film photovoltaic devices is that they require less active material, a secondary benefit is that they are ideally suited for the creation of large modules. Last but not least they allow, if a flexible substrate is provided, to fabricate light-weight, flexible and foldable modules. These qualities provide them a guaranteed path to lowering the €/W cost of PV modules, and if they attain high efficiencies, they will be able to obtain a sizable market share. The copper-indium-gallium-selenium alloy CuInGaSe2 (CIGS) thin-film technology has the highest conversion efficiency (above 23%), but its industrial development could be restricted by the current rate of global indium production. A possible rival to current solar cell technology is the Cu2ZnSnS4 (CZTS) solar cell. The CZTS’s absorption coefficient is on the order of 104 cm-1: the straight band gap is within the 1.0-1.5 eV region which is ideal for solar cells. One micrometre thick film may effectively function as photocurrent generator and absorb nearly all of the photons in the solar spectrum. As a result, the cost of a solar cell's material can be significantly decreased by utilizing elements that are abundant on Earth. Making a CZTS film involves several different processes, including spray deposition of the precursor and subsequent sulfurization, or reactive co-evaporation, or precursor evaporation and subsequent sulfurization, or spray pyrolysis, or co-sputtering, or PLD (pulsed laser deposition), or sol-gel, or spin coating, or and electrodeposition and so on. This thesis details several investigations into the effects of CZTS manufacturing settings (by non-vacuum processes), such as drying time and annealing temperatures and, on the structure and optical characteristics. In the first chapter the project is presented, with also a brief introduction to renewable energy, the physical principles of how a photovoltaic cell work and the structure of kesterite. Chapter II introduces different strategies for the preparation of CZTS based solar cells. The third chapter illustrates the several characterisation techniques applied in this work. The subsequent chapters present the results of extensive research on the synthesis, characterization, and optimization of kesterite thin films and their application as absorber layers in photovoltaic devices. The study covers various aspects such as deposition techniques, post-deposition treatments, device fabrication and optimization, and analyses the impact of these factors on the photovoltaic performance of finished solar cells. Drying time and annealing temperature was shown to affect the stoichiometry and the morphology of the compound, generating secondary phases. This strongly influences the final efficiency of the devices and the behaviour under accelerated stability test. The present thesis provides a contribution in the understanding of low-cost non-vacuum preparation of kesterite absorbers. We obtained a final efficiency of 7.1% by doping with germanium, and over 8% with a doping solution of cadmium (this result is under patent approval)
A simple method for Ge incorporation to enhance performance of low temperature and non-vacuum based CZTSSe solar cells
No full textDespite the slow efficiency development, Cu2ZnSn(S,Se)4 still is a promising absorber material for solar cells for its easy and low cost way of fabrication and the abundance of its elements. Similarly, also CdTe faced a long period when the record efficiency would not improve over 16.5% until a different paradigm was introduced. CZTSSe, compared to other absorbers, has the advantage that can be successfully made by solution-based growth techniques which are unique for their low cost. However this is meaningful only if selenization process is not done at high temperatures and without complicated processes. So we have optimized an easy, low cost, non-vacuum fabrication process for Cu2(Zn,Sn)(S,Se)4 thin-film absorber layers by spin coating of precursor and subsequent lower temperature selenization. A precursor solution is deposited on a Mo coated glass and the stack is then annealed below 450 °C in Se atmosphere and without the application of toxic hydrazine. With this process, we have already presented efficiencies of around 5.5%, but in this work, we introduce a simple impurity inclusion process by treating the surface of the precursor film with chlorine-based compound containing either Na, K or Ge. This allows to improve the open circuit voltage and the current density, with an increase in efficiency of 25% compared to the non-treated sample. The structural modifications are addressed by X-ray diffraction, Raman spectroscopy, atomic force microscopy and scanning electron microscopy. Current-voltage, capacitance-voltage and drive level capacitance profiling are used to analyse performance and defect density in the finished devices
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
Analysis of the drying process for precursors of Cu2ZnSn(S,Se)4 layers by low cost non vacuum fabrication technique
No full textCu2ZnSn(S,Se)4 solar cells were fabricated by a non-vacuum solution-based spin coating technique followed by annealing in selenium atmosphere without H2S treatment. The effects of the drying time after spin coating on physical and electrical properties of the cells were investigated. Structural and morphological properties were investigated by X-ray diffraction, Raman spectroscopy, energy dispersive X-ray analysis, atomic force microscopy and scanning electron microscopy. The physical properties, in terms of stoichiometry, crystal structure, morphology and orientation of the grains were shown to be influenced by the different drying times. Consequently, current-voltage characteristics show that the drying time of the precursors has a significant involvement in the device performance. The highest efficiency has been measured for 5 min drying time (with a 4.73% efficiency is obtained with Voc = 320 mV, Jsc = 28.6 mA/cm2 and FF = 52%), while samples with longer or shorter drying time have lower efficiencies. A further increase in efficiency, exceeding 5%, is obtained by inserting a contact grid on the front contact. Also accelerated stability tests (performed in a black box with one sun illumination at 80 degrees C) show different effects in light soaking, almost no degradation is observed for all the three cases. In this paper we highlight the connection of the different physical to the electrical properties generated just by the different drying times of the precursor for the CZTS absorbers
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
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