1,720,964 research outputs found
Characterization of n-type Silicon Oxide for Use in Thin Film Solar Cells
No full textThis thesis studied the characteristics and applications of n-type silicon oxide (SiOx) produced through plasma enhanced chemical vapor deposition were studied through. n-type SiOx has shown excellent results in various applications of solar cell technology including back reflectors and intermediate reflecting layers. These results can aid in making amorphous silicon cells thinner. Thinner cells are not only cheaper and less resource intensive but are known to be much less susceptible to degradation, which is a major research goal in amorphous silicon solar cells. This thesis used three experiments to characterize and utilize n-type SiOx. First, the effects of varying deposition parameters of SiOx films were analyzed. SiOx layers were then applied as back reflectors of p-i-n amorphous silicon solar cells. Finally, SiOx was integrated into a two-period, one-dimensional photonic crystal. Forward power, pressure, CO2 flow and PH3 flow during deposition were varied to study their effects on SiOx films. Optical and electrical characteristics, as well as the deposition rate, of the films were measured as each deposition parameter was varied. Raman spectroscopy was also used to analyze the crystalline silicon structures in the material. These measurements showed that an increase in the oxygen content of SiOx enhanced its optical characteristics, while decreasing its electrical characteristics. CO2 flow as well as power and pressure had significant an impact on the oxygen content. Furthermore, it was found that increasing PH3/SiH4 flow ratio above 0.024 decreased the doping concentration of the SiOx film and had adverse effects on both the conductivity and activation energy of the films. Raman spectroscopy results suggested that the SiOx contained 5-7 nm crystalline silicon features. SiOx layers were deposited on amorphous silicon cells using both a p-i-n-SiOx configuration, as well as a p-i-SiOx configuration that contained no n-type amorphous silicon layer. In addition to varying the SiOx deposition parameters, the thickness of the n-type amorphous silicon layer was also varied. These cells were measured in a solar simulator and an external quantum effficiency setup. The p-i-n-SiOx solar cells achieved an initial efficiency of 10.8 % and a JSC of 16.65 ma/cm2. This was a relative efficiency enhancement of 15.3 % and a relative JSC enhancement of 17.5 % over standard p-i-n solar cells. p-i-SiOx cells achieved an initial efficency of 9.85 % and JSC of 16.55 mA/cm2. Degradation tests showed stabilized efficiencies of 8.2 % for p-i-n-SiOx cells and 7.9 % for p-i-SiOx cells. The external quantum efficiency results showed significant improvement of p-i-n-SiOx cells over p-i-n cells in the red spectra, which are attributed to enhanced reflection. There was also significant improvement in the blue spectra, which is attributed to enhanced electron collection at the back of the solar cell. SiOx was also integrated into a photonic crystal using n-type amorphous silicon as the second material. The photonic crystal was designed through careful tuning using the Advanced Semiconductor Analysis (ASA) simulation package. The results were very promising and showed how photonic crystals can be finely tuned for specific solar cell applications such as an intermediate reflecting layer for a micromorph cell.Sustainable Energy TechnologiesElectrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
Doped nanocrystalline silicon oxide for use as (intermediate) reflecting layers in thin-film silicon solar cells
No full textIn summary, this thesis shows the development and nanostructure analysis of doped silicon oxide layers. These layers are applied in thin-film silicon single and double junction solar cells. Concepts of intermediate reflectors (IR), consisting of silicon and/or zinc oxide, are applied in tandem cells. Multi-stack Bragg reflector IRs are tested in tandem cells, increasing the top cell current output. Finally, mechanical polishing is applied on intermediate reflectors, creating asymmetrically textured IRs. Doped silicon oxide layers have proven their versatility as multipurpose layers in thin-film silicon solar cells. In chapter 3, the search for device grade n- and p-doped silicon oxide material is described. The nanostructure of silicon oxide films with a wide array of optical and electrical properties is studied in detail by TEM, Raman, FTIR and XPS. Silicon oxide is found to be a very heterogeneous material with complex nanostructure. Both the amorphous and crystalline phases of silicon oxide are studied in detail. Differences are found between the p- and n-doped materials. It is found that the n-doped material has a nanostructure of silicon crystal grains embedded in an amorphous silicon oxide matrix. The p-doped material, however, contains silicon filaments in an amorphous silicon oxide matrix. These filaments are of intrinsic amorphous silicon with crystalline silicon grains. Intrinsic amorphous silicon is mainly responsible for good conductivity in both n-doped and p-doped silicon oxide, however, minimum crystalline content is also required. Finally, the relations between each phase and element content is related to optical and electrical properties. N-doped silicon oxide used as a back reflector in single junction solar cells reflects unabsorbed light back into the absorber layer, increasing its current output. The blue part of the spectrum is absorbed in one pass, therefore the response in the red part of the spectrum is expected to increase. However, an increase in the blue part of the spectrum is observed as well and is the topic of chapter 4. This increase is attributed to a combination of factors, but mostly to the prevention of a native oxide formation on the standard a-Si:H n-layer. The standard n-layer is covered with the n-doped silicon oxide layer which prevents the standard layer from oxidizing in ambient air. The silicon oxide also provides a better contact interface with silver. Other factors increasing the blue response include: 1. The lower activation energy of n-doped silicon oxide in comparison with the standard a-Si:H n-layer. 2. The changing of the band states due to the larger bandgap of n-doped silicon oxide in reference to n-doped a-Si:H. 3. The thinner a-Si:H n-layer as the one in the reference cell is twice as thick. 4. The lower parasitic plasmonic absorption in the silver back contact due to the common interface with silicon oxide. P-doped silicon oxide exhibits anti-reflective properties, increasing cell current output in the blue part of the spectrum as well. An initial efficiency of 11.4% is achieved with the application of both p- and n-doped silicon oxide layers in a single junction a-Si:H solar cell. Intermediate reflector concepts are explored in chapter 5. Distributed Bragg Reflectors (DBR) have tunable reflective properties and are an interesting candidate for intermediate reflectors in tandem cells. They exhibit nearly the same reflectance range under various angles of incidence. DBRs can be easily designed with the help of optical simulation software such as ASA. The design sequence is as follows: 1. The desired reflectance range inside a solar cell is simulated by varying the thickness of each material. 2. This stack is then simulated in a glass – air environment. 3. The stack is deposited on a glass substrate. 4. The measured reflectance is compared with the air – glass simulation. If a good fit is achieved, the DBR will give the desired simulated reflectance inside the cell. DBRs greatly enhance the top cell current in a tandem cell, reaching up to 13,5 mA/cm2 in a 175 nm-thick a-Si:H layer. Current matching and lowering of Voc remain issues. Texture control in the IR is important in order to provide good light scattering for both the top and bottom cells of a tandem and to provide a good substrate for the growth of a defect-free nanocrystalline absorber layer. An approach to modify the texture of ZnO serving as an asymmetric IR in a tandem cell is developed. Because of the excellent performance of the top amorphous silicon cell deposited on an Asahi VU substrate, it is beneficial to keep this substrate texture for the top cell and integrate different textures (with larger surface features) in the layers processed after the top cell. Two approaches to create an asymmetrically-textured IR are chosen: wet etching and mechanical polishing. The wet etching approach is done with two dilution levels of HCl. Then the IR interface facing the top cell has a typical Asahi VU texture while the IR interface facing the bottom cell has larger surface features beneficial for long-wavelength scattering. The second approach is about applying mechanical polishing to silicon oxide and ZnO IRs. This approach successfully flattened the Asahi-induced texture, leaving it in the IR interface facing the top cell and on the other flat side allowing higher-quality nc-Si:H growth.Electric Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
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
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