105,046 research outputs found
Wet chemical passivation of interface defects in a a SI H c Si heterojunction solar cells with randomly distributed pyramids
No full textWET CHEMICAL PASSIVATION OF INTERFACE DEFECTS IN a SI H c SI HETEROJUNCTION SOLAR CELLS WITH RANDOMLY DISTRIBUTED PYRAMIDS H. Angermann, J. Rappich, K. v. Maydell, E. Conrad, I. Sieber, D. Schaffarzik and M. Schmidt Hahn Meitner Institut Berlin, Kekul str.5, D 12489 Berlin Corresponding author H. Angermann, Hahn Meitner Institut Berlin HMI , Kekul str.5, D 12489 Berlin, Tel 49 30 8062 1368, Fax 49 30 8062 1333 e mail angermann helmholtz berlin.de ABSTRACT Two non destructive, very surface sensitive tech niques, the large signal field modulated surface photovoltage SPV method and pulsed photoluminescence spectroscopy PL were applied to investigate both wet chemically treated substrate surfaces and a Si c Si interfaces. In order to prepare silicon substrates with randomly distributed pyramids without surface micro roughness and native oxide contamination and to passivate them during the technological process, we investigated special combinations of wet chemical etching and cleaning procedures. Compared to conventional pre treatments, significantly lower densities surface states and recombination loss were achieved on silicon substrates textured with randomly distributed upside pyramids and on the resulting a Si c Si in terfaces after deposition. It was shown that the open circuit voltage Voc and solar cell efficiency of TCO a Si H n c Si p Al solar cells are mainly influence by the preparation induced morphology and electronic properties of substrate surface. Keywords silicon substrates, defect density, wet chemical pretreatmen
Der Stein von Olderdissen. Ein Zeugnis bäuerlicher Kultur Ravensbergs aus dem Jahr 1544
No full textAngermann G, Rüthing H. Der Stein von Olderdissen. Ein Zeugnis bäuerlicher Kultur Ravensbergs aus dem Jahr 1544. Jahresbericht des Historischen Vereins für die Grafschaft Ravensberg. 2005;90:177-217
Software Representation for Heterogeneous Data Sources Within A Probabilistic Framework
No full textIn this paper we present a framework for the representation of location information from various sources, such as satellite navigation systems, wireless positioning technologies, beacons, indoor navigation systems, human input, etc.
These sources all operate at various degrees of accuracy and often suffer from independent errors. Their output, in terms of the location, can be represented more generally as a probability density distribution (PDF) of the location over a two or three dimensional space - typically Cartesian or other co-ordinates. Combining two or more such PDFs yields a more accurate PDF of the location and improves navigation under difficult circumstances such as indoors or in fading environments. To allow practical deployment of such a framework we define a simple software interface, using the Java programming language, that relies on the transfer of software objects and class files describing the individual
PDFs. A number of different positioning sources can thus describe their individual location PDF using a Java class and object, and pass this to other (sub-)devices that have no a-priori knowledge of this PDF for combination
with other PDFs
Arithmetic Team of 1919
No full textThis is a photograph of the Egg Harbor City Arithmetic Team of 1919. The contest was between the teams of Atlantic County, NJ. W. H. Pollack was the teacher.
The banner seen in the photograph reads "Atlantic County, NJ. Awarded Annually for the Highest Team Average in Arithmetic."
Pictured are: Emma Angermann, Edward Hand, Dorothy Wills, Paul Meuther, and Theresa Cairone
A Novel Movement Model for Pedestrians Suitable for Personal Navigation
No full textIn this paper a combination of two movement
models, operating at the microscopic level and suitable
for pedestrian navigation is developed and tested. The
constituents are a Stochastic Behavioral Movement Model
to characterize more random motion and a Diffusion
Movement Model to characterize a geographic goal a
pedestrian might walk towards. A top-level Markov
process is used to determine whether to currently use the
stochastic behavioral or the diffusion model; therefore,
the model switches between motion that is more goal
oriented (diffusion model) or stochastic.
Advantages and disadvantages of both individual
constituent models are demonstrated and discussed. The
combined movement model is demonstrated to achieve
the best of both worlds and to avoid the problems
associated with using a single model. The properties and
the performance of the resulting model will be explained
in details
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
Optimisation of electronic interface properties of a Si H c Si hetero junction solar cells by wet chemical surface pre treatment
No full textOptimisation of electronic interface properties of a Si H c Si hetero junction solar cells by wet chemical surface pre treatment H. Angermann , L. Korte1, J. Rappich1, E. Conrad1, I. Sieber1, M. Schmidt1, K. Hübener2, J. Hauschild2 1 Hahn Meitner Institut, Abt. Siliziumphotovoltaik; Kekul stra e 5, D 12489 Berlin, Germany 2Freie Universitaet Berlin, FB Physik, Arnimallee 14, 14195 Berlin Abstract The relation between structural imperfections at structured silicon surfaces, energetic distribution of interface state densities, recombination loss at a Si H c Si interfaces and solar cell characteristics have been intensively investigated using non destructive, surface sensitive tech niques, surface photovoltage SPV and photoluminescence PL measurements, atomic force microscopy AFM and electron microscopy SEM investigations. Sequences of wet chemical oxidation and etching steps were optimised with respect to the etching behaviour of Si 111 pyramids. Special wet chemical smoothing and oxide removal procedures for structured substrates were developed, in order to reduce the preparation induced surface micro roughness and density of electronically active defects. H termination and passivation by wet chemical oxides were used to inhibit surface contamination and native oxidation during the technological process. We achieved significantly lower micro roughness, densities of surface states Dit E and recombination loss at a Si H c Si interfaces on wafers with randomly distributed pyramids, compared to conventional pre treatments. For amorphous crystalline hetero junction solar cells ZnO a Si H c Si BSF Al , the c Si surface becomes part of the a Si H c Si interface, whose recombination activity determines cell performance. With textured substrates, the smoothening procedure results in a significant increase of short circuit current, fill factor and efficiency. Keywords a Si H c Si hetero junction solar cells, wet chemical pre treatment, silicon substrates, interface state density, recombination loss, surface photovoltage, photoluminescence, atomic force microscop
Development and optimization of a Si H c Si heterojunction solar cells completely processed at low temperatures
No full textSubject Number 2 Crystalline Silicon Solar Cells and Materials Technology Development and optimization of a Si H c Si heterojunction solar cells completely processed at low temperatures K. v. Maydell, E. Conrad, H. Angermann, C. Schubert, R. Stangl and M. Schmidt Hahn Meitner Institut Berlin, Kekul str.5, D 12489 Berlin Corresponding author K. v. Maydell, Hahn Meitner Institut Berlin HMI , Kekul str.5, D 12489 Berlin, Tel 49 30 8062 1350, Fax 49 30 8062 1333 e mail maydell helmholtz berlin.de We report on the development and optimization of amorphous crystalline silicon a Si H c Si solar cells which where completely processed at temperatures below 230 C. Both doping sequences were investigated a Si H n c Si p and a Si H p c Si n . No intrinsic buffer layers between the a Si H and the c Si wafer were used. To reach high efficiencies a low temperature a Si H rear side has been developed. Using surface photovoltage measurements it can be shown that a highly doped a Si H layer causes the formation of a back surface field at the rear side of the wafer. A simulation study, using our simulation program AFORS HET, shows that the potential of the efficiency of this kind of solar cells is larger 23 using the measured defect characteristics of the a Si H layers. The most dominating loss mechanism is recombination at the interface. The highest efficiencies obtained so far are 17.4 on p type and 18.2 on n type substrates. For reaching efficiencies towards 20 the interface states density of the a Si H c Si heterojunction on the front and back side has to be minimized or their incorporation into the recombination process has to be suppressed. Especially for textured substrates this is most important since VOC is reduced by about 20 mV compared to polished substrates. This can be done by different ways I Using appropriate preconditioning of the wafer, the surface states density can be reduced which results in a low interface states density of the resulting heterojunction. II The growth conditions of the a Si H layer on the c Si wafer have to be optimized in order to reduce the interface states density. We report on two different preconditioning methods prior to the a Si H deposition Hydrogen plasma passivation and wet chemical treatment of the c Si wafer. A H plasma passivation leads to a reduction in the effective recombination at the a Si H c Si interface as shown by transient surface photovoltage measurements. This causes an enhancement in the solar cells open circuit voltage up to 30mV on textured substrates. The standard wafer cleaning sequence is composed of a RCA cleaning followed by an HF dip. This usually leads to a rough surface in atomic scale. We tried to smoothen the surface using an additional wet chemical process step. This causes a reduction in the surface states density of the c Si wafer, a decrease of recombination at the a Si H c Si interface and thus to an enhancement in VOC. We will present the results of a Si H c Si solar cells on n type and p type c Si wafers with the combination of optimized wet chemical and H plasma pre treatments and a Si H deposition conditions
Surface states and recombination loss on wet chemically passivated Si studied by Surface Photovoltage SPV and Photoluminescence PL
No full textSurface states and recombination loss on wet chemically passivated Si studied by Surface Photovoltage SPV and Photoluminescence PL H. Angermann a, J. Rappich b Hahn Meitner Institut, Kekul stra e 5, D 12489 Berlin, Germany The miniaturisation of circuit patterns and the increasing level of density, integration and performance require prepa ration of defect and contamination free thin film structures with excel lent electronic prop erties. The preparation and characterisation of extremely clean, smooth and undamaged silicon substrate sur faces are very important issues, because the interface takes up a greater part of the device. Interface defects, resulting in rechargeable states become increasingly more critical to quality of thin oxide, epitaxial, and passivation layers. This paper reports investigation of various conventional and newly developed wet chemical cleaning and passivation methods on Si 111 and Si 100 substrates, with regard to preparation induced surface states und recombination behaviour. The energetic distributions of surface states Dit E were determined by a pulsed field modulated SPV method, firstly described in 1968 by Heilig [ ]. The SPV technique has the general advantage that the measurements can be carried out repeatedly during the wet chemical treatment without any contact prepa ra tion, using a mica foil dielectric spacer. To determine the interface state density Dit E a varying electric field perpendicular to the surface is applied, which changes the surface potential amp; 61510;s continuously as a function of the field voltage UF. Additionally, pulsed photoluminescence PL was applied to inspect the surface passivation by changes in the band band related PL of Si due to quenching of the PL by surface defects as described in refs. [ , ]. Wet chemical H termination procedures generally include two essential steps the formation of a silicon oxide interfaces by oxidizing solutions and the subsequent removal of these native oxide layer by HF or NH4F containing solutions. Therefore, the prepa ra tion induced micro roughness of H terminated silicon surfaces, results from the course of two different chemical processes the wet chemical oxidation of the silicon surface as well as the etching behaviours of silicon oxide and silicon substrate. As recently reported, the density and the character of states on the wet chemically passivated surface are closely related to the surface micro roughness and stage of oxidation [ ]. In order to further elucidate the influence of both, wet chemical oxidation and final etching process, all Si 111 and Si 100 samples were initially cleaned by the conventional RCA process and etched by HF 1 dip for 1 minute and subsequently oxidized again applying different oxidizing solutions and H terminated by HN4F and HF solution. It was shown, that simultaneous SPV and PL measurements can be serve as a very sensitive tool for repeatedly detection of surface electronic properties on Si wafers during wet chemical preparation processes. The influence of both, the initial interface roughness and surface roughness after the final etching step in HF and NH4F containing solutions on surface electronic properties has been investigated on Si 100 and Si 111 substrates during the technological process. It was shown, that the first problem is to decrease the initial interface roughness between substrate and wet chemical oxide layer applying non aggressive oxidizing solutions under controlled conditions. To avoid additional increase of surface states during the oxide removal, the HF containing etching solution has to be choose considering the Si surface orientation. To minimize the densities of rechargeable surface states and the recombination lost on H terminated surfaces, we optimised the sequence of preparation steps for different substrate applications
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