Optimierung der Vorderseitenmetallisierung und des Emitters für hocheffiziente industrielle Silizium Solarzellen

[no abstract

Contribution Barriers to Open Source Projects

Contribution barriers are properties of Free/Libre and Open Source Software (FLOSS) projects that may prevent newcomers from contributing. Contribution barriers can be seen as forces that oppose the motivations of newcomers. While there is extensive research on the motivation of FLOSS developers, little is known about contribution barriers. However, a steady influx of new developers is connected to the success of a FLOSS project. The first part of this thesis adds two surveys to the existing research that target contribution barriers and motivations of newcomers. The first exploratory survey provides the indications to formulate research hypotheses for the second main survey with 117 responses from newcomers in the two FLOSS projects Mozilla and GNOME. The results lead to an assessment of the importance of the identified contribution barriers and to a new model of the joining process that allows the identification of subgroups of newcomers affected by specific contribution barriers. The second part of the thesis uses the pattern concept to externalize knowledge about techniques lowering contribution barriers. This includes a complete categorization of the existing work on FLOSS patterns and the first empirical evaluation of these FLOSS patterns and their relationships. The thesis contains six FLOSS patterns that lower specific important contribution barriers identified in the surveys. Wikis are web-based systems that allow its users to modify the wiki's contents. They found on wiki principles with which they minimize contribution barriers. The last part of the thesis explores whether a wiki, whose content is usually natural text, can also be used for software development. Such a Wiki Development Environment (WikiDE) must fulfill the requirements of both an Integrated Development Environment (IDE) and a wiki. The simultaneous compliance of both sets of requirements imposes special challenges. The thesis describes an adapted contribution process supported by an architecture concept that solves these challenges. Two components of a WikiDE are discussed in detail. Each of them helps to lower a contribution barrier. A Proof of Concept (PoC) realization demonstrates the feasibility of the concept

A comparison of the PAR Index based on analog plaster and plastic models respectively, as well as digital models in OnyxCeph and OrthoAnalyzer respectively

Zielsetzung: Ziel dieser Studie ist es, die Genauigkeit von konventionellen Gipsmodellen, analogen Kunststoffmodellen und digitalen Modellen in der OnyxCeph- und Ortho-Analyzer-Software zu untersuchen. Zum Vergleich wird dafür der durchschnittliche Peer Assessment Rating Index (PAR-Index) jeder Modellart ermittelt. Anschließend werden diese PAR-Werte mit denen des Ursprungsmodells verglichen, um eine Aussage darüber treffen zu können, welche Art der Abformung und Modellherstellung für die Modellanalyse in der Kieferorthopädie zu bevorzugen ist. Methodik: Ein Mastermodell wurde durch zwölf PAR-zertifizierte Behandler mittels PAR-Index vermessen und dessen Mittelwert gebildet. Anschließend erfolgte die Abformung des Mastermodells durch Alginat und mittels direkter Digitalisierung durch einen Intraoralscanner. Auf konventionellem Wege wurden Gipsmodelle hergestellt und der Scandatensatz wurde sowohl für den Druck von Kunststoffmodellen durch einen Stereolithografie-Drucker, als auch für die Modellerstellung in der OnyxCeph- und OrthoAnalyzer-Software genutzt. Die vier verschiedenen Modellarten wurden anschließend durch 120 Behandler aus drei verschiedenen Berufsgruppen – Kieferorthopäden, Studenten und Assistenten – vermessen und die ermittelten durchschnittlichen PAR-Werte der Gruppen mit dem des Mastermodells verglichen. Ergebnisse: Es konnten keine signifikanten Unterschiede zwischen den Mittelwerten des PAR-Index bei den Modellarten Mastermodell, Gipsmodell, Kunststoffmodell und den digitalen Modellen in OnyxCeph und OrthoAnalyzer festgestellt werden. Des Weiteren konnten keine signifikanten Unterschiede zwischen den Mittelwerten des PAR-Index bei den Behandlerarten Goldstandardvermesser, Kieferorthopäden, Studenten und Assistenten festgestellt werden. Schlussfolgerung: Alle vier Modellarten zeigen eine ausreichende Validität bei der Ermittlung des PAR-Index. Es konnten keine verbesserten Werte in Bezug auf Präzision und Richtigkeit beim konventionellen Modell im Vergleich zu den digitalen Modellen festgestellt werden. Die digitale Abformung und Modellanalyse ist somit als gleichwertig zur konventionellen analogen Abformung zu betrachten. Dieser Umstand sollte in Zeiten von ständiger Digitalisierung auch in der modernen Zahnarztpraxis Anwendung finden. Für eine umfassendere Bewertung in Bezug auf ökonomische und ökologische Faktoren sind weitere Studien wünschenswert.Objective: This study aims to investigate the accuracy of conventional plaster models, analog plastic models and digital models in OnyxCeph and OrthoAnalyzer. To examine this the average Peer Assessment Rating Index (PAR Index) of each model type is determined and compared to those of the original model to determine which form of impression and model is preferred for analysis in orthodontics. Methods: First, the measurement of one original (master) model were taken by twelve PAR-certified dentists using the PAR index and the mean thereof were calculated. Afterwards a conventional alginate impression and an intraoral scan of the master model were taken. Plaster models were produced and the scan data set was used for printing plastic models with a stereolithography printer as well as creating digital models in the OnyxCeph- and OrthoAnalyzer- software. Later on 120 examiners from three different professions - orthodontists, students and assistants - measured the four different types of models. Lastly the average PAR values for each group were compared to the primarily calculates mean measurement of the master model. Results: No significant differences were found between the average PAR index values of the master model, plaster model, acrylic model and the digital models in OnyxCeph and OrthoAnalyzer. Furthermore, no significant differences between the mean values of the PAR index were found for the examiners of gold standard, orthodontist, student and assistant. Conclusion: All model types show sufficient validity in determining the PAR Index. There were no improved values in terms of precision and correctness for the conventional model compared to the digital models. The digital impression and analysis could therefore be considered equivalent to the conventional method. In times of constant digitalization, the results of this study should be considered in modern dental treatment. Further studies should be done for a more comprehensive assessment in terms of economic and ecological factors

Fineline printing options for high efficiencies and low Ag paste consumption

In this paper, we investigate and compare three different fine line printing techniques for the silver front side metallization of industrial-type silicon solar cells: single print, dual print and print-on-print. We produce solar cells using the same screen or stencil aperture of 40 μm and about 92 fingers and obtain finger widths below 60 μm for all three approaches. The print-on-print process achieves the highest finger heights of 20 μm after firing but with quite strong finger height variation. In contrast, the dual printed fingers have a very flat surface with a finger height of 14.5 μm which leads to the highest cross-section area of 530 μm2 of the three techniques. The single print shows the lowest cross-section area of 390 μm2 due to the lowest average finger height. The measured finger line resistance correlates with the finger cross-section area. The dual print allows us to use a non-firing through bus bar paste which increases the V oc by 2 mV and hence achieves the highest efficiency of 19.1% using full-area Al-BSF cells. Due to an optimized bus bar screen print in combination with only 30 μm finger aperture, the dual print has the lowest Ag paste consumption of only 75 mg/wafer, one of the lowest Ag paste consumption that has been reported so far. A first batch of PERC solar cells with dual-printed Ag front contacts shows efficiencies up to 19.6%.German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety/0325296SolarWorld Innovations GmbHRENA GmbHSINGULUS TECHNOLOGIES AGHeraeus Precious Metal

Optimized stencil print for low Ag paste consumption and high conversion efficiencies

We evaluate industrial-type PERC solar cells applying a dual printed front grid with stencil printed Ag fingers. We vary the Ag paste consumption for the finger print between 8.4 mg and 120.4 mg per 156 x 156 mm(2) wafer (weighted after printing before drying) by using polyurethane squeegees with different shore hardness as well as a metal squeegee and by varying the printing pressure to obtain different finger heights. The busbar consumes additional 19.5 mg Ag paste. We obtain average finger heights from 5.9 mu m up to 24.3 mu m for 55 mu m to 65 mu m wide fingers. The resulting PERC solar cells show an average efficiency of 20.2% for finger paste consumptions above 60 mg. In contrast, a strong reduction of the conversion efficiency with less than 60 mg finger paste consumption is observed since the increased series resistance reduces the FF. By analytical modelling, we compare the calculated series resistance to the experimental data and observe a good accordance for more than 40 mg finger paste consumption whereas the experimental series resistance slightly exceed the modelled values below 40 mg. In addition, we use numerical simulations to investigate the series resistance dependence on the finger height which shows higher experimental values for finger height below 10 mu m. The deviation of the measured series resistance and the two modelled cases is mostly due to inhomogeneous distribution of finger height profiles and finger interruptions on the solar cells with front finger paste consumption of less than 40 mg. For finger paste consumption below 60 mg, we find that also the specific contact resistance increases. A physical model of the root cause for this dependence still has to be found

Record low ag paste consumption of 67.7 mg with dual print

We investigate and compare three different fine line printing techniques for the silver front side metallization of industrial-type silicon solar cells: single print, dual print and print-on-print. We obtain finger heights of 5.6 μm for single print, 9.5 μm for dual print and 15.1 μm for print-on-print as well as finger width between 46.2 μm and 61.3 μm. We process PERC solar cells with dual print and print-on-print. For the dual print, we test two different bus bar designs, a standard rectangular shaped bus bar and a segmented bus bar. The resulting PERC solar cells achieve conversion efficiencies of 19.8% for dual print and print-on-print. The dual print with segmented bus bar design reduces the Ag paste consumption to 67.7 mg, measured after printing prior to drying. To our knowledge, this is the lowest front side Ag paste consumption that has been reported so far. Additionally, we model optimum Ag finger width in dependence of electrical and geometrical parameters. We find that even when assuming very optimistic parameters, the optimum finger width of 26 μm is just a factor of two lower compared to the state of the art technology today.German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety/0325296SolarWorld Innovations GmbHRENA GmbHSINGULUS TECHNOLOGIES AGHeraeus Precious Metal

Tuning the thermal conductivity of silicon nanowires by surface passivation

Using large scale molecular dynamics simulations, we study the thermal conductivity of bare and surface passivated silicon nanowires (SiNWs). For the smaller cross-sectional widths $w$, SiNWs become unstable because of the surface amorphousization and even evaporation of a certain fraction of Si atoms when $w \leq 2$ nm. Our results suggest that the surface (in--)stability is related to a large excess energy $\Delta$ of the surface Si atoms with respect to the bulk Si. This is because the surface Si atoms being less coordinated and having dangling bonds. As a first step of our study, we propose a practically relevant method that uses $\Delta$ as a guiding tool to passivate these dangling bonds and thus stabilizes SiNWs. The surface stabilization is achieved by passivation of Si atoms by hydrogen or oxygen. These passivated SiNWs are then used for the calculation of the thermal conductivity coefficient $\kappa$. While the expected trend of $\kappa \propto w$ is observed for all SiNWs, surface passivation provides an added flexibility of tuning $\kappa$ with the surface coverage concentration $c$ of passivated atoms. Analyzing the phonon band structures via spectral energy density, we discuss separate contributions from the surface and the core to $\kappa$. The effect of passivation on SiNW stiffness is also discussed

Correction: Tuning the optical properties of the metal-organic framework UiO-66 via ligand functionalization

The authors apologise that the comparison of calculated (HSE06) and experimental band gaps shown in Fig. 3 were incorrect, the experimental values did not match the presented UV-Vis spectra and Tauc plots. The figure is corrected as follows: The corrections shown here do not affect the conclusions in the paper. (Figure Presented).The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers

Tuning the optical properties of the metal-organic framework UiO-66 via ligand functionalization

Metal-organic frameworks (MOFs) are a promising class of materials for optical applications, especially due to their modular design which allows fine-tuning of the relevant properties. The present theoretical study examines the Zr-based UiO-66-MOF and derivatives of it with respect to their optical properties. Starting from the well-known monofunctional amino- and nitro-functionalized UiO-66 derivatives, we introduce novel UiO-66-type MOFs containing bifunctional push-pull 1,4-benzenedicarboxylate (bdc) linkers. The successful synthesis of such a novel UiO-66 derivative is also reported. It was carried out using a para-nitroaniline (PNA)-based bdc-analogue linker. Applying density functional theory (DFT), suitable models for all UiO-66-MOF analogues were generated by assessing different exchange-correlation functionals. Afterwards, HSE06 hybrid functional calculations were performed to obtain the electronic structures and optical properties. The detailed HSE06 electronic structure calculations were validated with UV-Vis measurements to ensure reliable results. Finally, the refractive index dispersion of the seven UiO-66-type materials is compared, showing the possibility to tailor the optical properties by the use of functionalized linker molecules. Specifically, the refractive index can be varied over a wide range from 1.37 to 1.78

Loss analysis and improvements of industrially fabricated Cz-Si solar cells by means of process and device simulations

We model currently fabricated industrial-type screen-printed boron-doped Cz silicon solar cells using a combination of process and device simulations. The model reproduces the experimental results precisely and allows us to predict both the efficiency gain after specific cell improvements and the associated thermal budgets. Separating the resistive losses (evaluated for various contributions) from the recombination losses (evaluated in different device regions) allows us to forecast the improvements of the emitter and the rear side necessary such that the recombination losses in the base dominate. We predict that to increase cell efficiency considerably beyond 19.7 %, the base material needs to be improved