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Nanocrystalline Layers for Silicon Heterojunction (SHJ) and SHJ/Perovskite Tandem Devices
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Lifetime-limiting defects in monocrystalline silicon
No full textThis thesis discusses studies performed by the author at the Fraunhofer Institute for Solar Energy Systems, ISE in cooperation with the Freiburg Materials Research Center, FMF. The main achievements are:- A new measurement technique was developed that allows the investigation of the distribution of interstitial oxygen atoms in silicon wafers. The method is based on photoluminescence imaging and the measurement of resistivity changes upon annealing at 450 °C. This results in a high lateral resolution on full samples with reasonable effort. It thereby opens up pathways to improve the understanding of the distribution of impurities during crystal growth. Furthermore, the method can be applied to very thin wafers without loosing precision. It is therefore feasible for typical sample thicknesses in photovoltaic research, where application of infrared absorption spectroscopy becomes problematic.- An extensive literature review of the broad field of studies of the light-induced degradation caused by boron-oxygen defects is given. The review provides an overview over aspects that were subject of vivid discussions in literature. It reduces the pronounced fragmentation of the scientific discourse in the field by indentifying established and controversial findings in literature.- Detailed experiments to investigate the activation kinetics of boron-oxygen defects were performed on compensated n-type silicon. The results provide unambiguous confirmation of the strong dependence of the activation rates on the concentration of holes during illumination. This influence was demonstrated to apply to both, the fast and the slow activation processes. This finding indicates the involvement of two holes in both defect state transitions.- The recombination activity of boron-oxygen defects was investigated in dependence of sample doping and injection conditions. The experiments provide strong evidence that boron-oxygen defects introduce at least two energetic levels in the silicon band gap that interact during recombination
Lifetime-limiting defects in monocrystalline Silicon
No full textThis thesis discusses studies performed by the author at the Fraunhofer Institute for Solar Energy Systems, ISE in cooperation with the Freiburg Materials Research Center, FMF. The main achievements are: A new measurement technique was developed that allows the investigation of the distribution of interstitial oxygen atoms in silicon wafers. The method is based on photoluminescence imaging and the measurement of resistivity changes upon annealing at 450 °C. This results in a high lateral resolution on full samples with reasonable effort. It thereby opens up pathways to improve the understanding of the distribution of impurities during crystal growth. Furthermore, the method can be applied to very thin wafers without loosing precision. It is therefore feasible for typical sample thicknesses in photovoltaic research, where application of infrared absorption spectroscopy becomes problematic. An extensive literature review of the broad field of studies of the light-induced degradation caused by boron-oxygen defects is given. The review provides an overview over aspects that were subject of vivid discussions in literature. It reduces the pronounced fragmentation of the scientific discourse in the field by identifying established and controversial findings in literature. Detailed experiments to investigate the activation kinetics of boron-oxygen defects were performed on compensated n-type silicon. The results provide unambiguous confirmation of the strong dependence of the activation rates on the concentration of holes during illumination. This influence was demonstrated to apply to both, the fast and the slow activation processes. This finding indicates the involvement of two holes in both defect state transitions. The recombination activity of boron-oxygen defects was investigated independence of sample doping and injection conditions. The experiments provide strong evidence that boron-oxygen defects introduce at least two energetic levels in the silicon band gap that interact during recombination. A light-induced degradation of the charge carrier lifetime in p-type float-zone silicon was observed at elevated temperature and studied in detail. The investigations indicate that the effect arises from bulk defects involving hydrogen introduced from dielectric surface passivation layers. Several similarities to a light-induced degradation at elevated temperature in multicrystalline silicon are observed. A long-term stability test of several passivation schemes involving aluminium oxide was performed. The experiment demonstrates that the good passivation quality of such layers is stable for illumination durations above 1000 hours at elevated temperature
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
High Minority Charge Carrier Lifetimes in Crystalline Silicon - Auger, Radiative and Surface Recombination
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