196,004 research outputs found
A computerised data handling procedure for defect detection and analysis for large area substrates manufactured by roll-to-roll process
No full textThe development of optical on-line/in-process surface inspection and characterisation systems for flexible roll to roll (R2R) thin film barriers used for photo-voltaic (PV) modules is a core research goal for the EU funded NanoMend project. Micro and nano scale defects in the ALD (atomic layer deposition) Al2O3 barrier coating produced by R2R techniques can affect the PV module efficiency and lifespan. The presence of defects has been shown to have a clear correlation with the water-vapour-transmission-rate (WVTR). Hence, in order to improve the PV cell performance and lifespan the barrier film layer must prevent water vapour ingress. One of the main challenges for the application of in process metrology is how to assess large and multiple measurement data sets obtained from an in process optical instrument. Measuring the surface topography over large area substrates (approximately 500 mm substrate width) with a limited field-of-view (FOV) of the optical instrument will produce hundreds/thousands of measurement files. Assessing each file individually to find and analyse defects manually is time consuming and impractical. This paper reports the basis of a computerised solution to assess these files by monitoring and extracting areal surface topography parameters. Comparing parameter values to an experimentally determined threshold value, obtained from extensive lab-based measurement of Al2O3 ALD coated films, can indicate the existence of the defects within a given FOV. This process can be repeated automatically for chosen parameters and the existence of defects can be indicated for the entire set of measurement files spontaneously without interaction from the inspector. A running defect log and defect statistics associated with the captured set of data files can be generated. This paper outlines the implementation of the auto-defect logging using advanced areal parameters, and its application in a proof of concept system at the Center for Process Innovation (UK) is discussed
Implementation of wavelength scanning interferometry for R2R flexible PV barrier films
No full textRoll to Roll manufacture of nano-scale thinf ilm layers faces the challenge of micro/nano-scale defects appearing in the films. Atomic Layer Deposition (ALD) coatings of aluminium oxide, Al2O3 are used as barrier layers for photovoltaic (PV) solar modules where the primary function of the barrier layer is to prevent the water vapour ingress to the PV cells. Barrier layer defects have been shown to have negative impact on the performance of the barrier layers. Poor barriers cause module degradation resulting in reduced PV efficiency and lifespan. In order to ensure the quality of manufacture of the barriers, defects should be detected during the barrier production process and the information used to optimise the production process. This paper introduces, as part of EU funded NanoMend project, a full solution for inspection of entire surface regions of Al2O3 barrier films across large area substrates. The solution principle is based on implementing an opto-mechanical in-process inspection system to measure the significant defects using a wavelength scanning interferometer (WSI) embedded within the film-rewinder stage and integrated with the substrate translation and kinematic stages. The opto-mechanical system allows full surface measurement over full substrate widths of approximately 0.5m. The system provides an auto-focus for the WSI with an accuracy and repeatability better than 6 µm at optimum optical alignment conditions. The system is combined with a porous air-bearing conveyor used to hold the film web at fixed height within the focal depth of WSI objective lens and with height variation of 3 µm is also presented as a case study to highlight the system capability
Metrology and Characterisation of Defects on Barrier Layers for Thin Film Flexible Photovoltaics
No full textTransparent barrier films such as aluminium-oxide (Al2O3) can be used as a barrier to oxygen and/or water vapor permeation and such layers are of increasing interest for the encapsulation of flexible PV modules. However, the existence of micro and nano-scale defects in the barrier surface topography has been shown to have the potential to facilitate water vapor ingress, thereby reducing cell efficiency and causing internal electrical shorts in the CIGS cells. Therefore, improvement of the quality of these barrier films is critical to reduce the susceptibility of these photovoltaic systems to environmental degradation. This paper reports on the development of a characterisation method for defect detection and then correlates this with measured water vapor transmission rates (WVTRs). The results show small numbers of large defects play the dominant role in determining the WVTR. A unified classification system for defects is proposed where the classification breaks down the defects types into four main functional groupings
In-line metrology for defect assessment on large area Roll 2 Roll substrates
No full textThis paper reports on the recent work carried out as part of the EU funded research and development project NanoMend. The project seeks to develop integrated process inspection, cleaning, repair for nano-scale thin films on large area substrates. Flexible photovoltaic (PV) films based on CIGS (Copper Indium Gallium Selenide CuInxGa(1-x)Se2) have been reported to have light energy conversion efficiencies as high as 19%. Their adoption has many advantages in terms of applications and in particular building integration. These CIGS based multi-layer flexible devices are fabricated on polymer film by the repeated deposition, and patterning, of thin layer materials using roll-to-roll processes (R2R), where the whole film is approximately 3μm thick prior to final encapsulation. The resultant films are lightweight and flexible however wide scale implementation is hampered by long term environmental degradation of efficiency due to water ingress to the CIGS modules through the polymer layers causing electrical shorts and corresponding efficiency drops. In order to prevent water ingress the PV modules are coated with a protective barrier layer of Al2O3 using atomic layer deposition (ALD) methods. Unfortunately defects in this layer have been shown to reduce efficiency over a period of time due to water vapour passage. The present work concentrates on defect detection and reports on the use of areal surface metrology to correlate defect morphology with water vapour transmission rate (WVTR) through the protective barrier coatings The use of advanced segmentation techniques is demonstrated where topographic information on functionally significant defects can be extracted and quantified. The work also reports on the deployment of new in line interferometric optical sensors designed to measure and catalogue the defect distribution and size where they are present in the 40nm thick barrier film. The sensors have built-in environmental vibration compensation and have been deployed on a demonstrator system at a Roll2Roll production facility
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
Process Practice and its Effects on Surface Defects on Flexible PV Barrier Films
No full textTo the present day, there is still an increasing interest in the development of Cu (In, Ga) Se2 (CIGS) thin film solar cells on flexible polyimide substrates. These cells offer advantages of low cost, light weight and excellent radiation hardness as well as facilitating building-integrated-photovoltaic (BIPV) applications. These solar cells typically consist of six different layers of thin film including; Ag / Transparent Conductive Oxide (TCO) of ZnO: Al /CdS/CIGS/Mo/Al2O3 [1]. The Al2O3 insulating layer is introduced into the structure of the solar cell in order to prevent diffusion of water vapour and oxygen to the CIGS layer. Hence, to optimize the photovoltaic (PV) module performance and lifespan, a study to understand the nature of surface defects in the Al2O3 barrier layer which allows water vapour and oxygen ingress to the active layer (CIGS) is required. Surface metrology techniques including; Optical Microscopy, White Light Scanning Interferometry (WLSI), Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) were employed for collecting data on PV barrier layers defects down to nm scale. Feature segmentation analysis methods proved to be an effective tool for discrimination between insignificant and the most significant features which are directly responsible for PV module degradation.
Keywords: Photovoltaics, Defects, Surface topography, ALD and WVTR
"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States" By M. Carey.
No full text"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States: containing bried sketches of the moral and political character of those states.
By M. Carey, member of the American philosophical, and of the American Antiquarian Society, and author of The Olive Branch, Cindiciae Hibernicae, essays on banking, on political economy, and on internal improvement.
To which are now added the English editor's comments on the subject; together with Important Advice to Emigrants, and Cautions Against Impositions Practiced in the Outports
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
Implementation of in Process Surface Metrology for R2R Flexible PV Barrier Films
No full textThin functional barrier layers of aluminum oxide (Al2O3) that are used particularly in photovoltaic (PV) modules to prevent the possibility of water vapor ingress should be applied over the entire PV surface without any defects. However, for barrier layer thicknesses
within the sub-micrometer range (up to 50 nm)
produced through the atomic layer deposition (ALD) method, it is common for defects to occur during the production process. To avoid defective barriers from being incorporated in the final PV unit, defects need to be detected during the barrier production process.
In this paper, the implementation of in process inspection system capable of detecting surface defects such as pinholes, scratches, or particles down to a lateral size of 3 μm and a vertical resolution of 10 nm over a 500 mm barrier width is presented. The system has a built-in environmental vibration compensation capability, and can monitor ALD-coated films manufactured using roll-to-roll (R2R) techniques. Ultimately, with the aid of this in process measurement system, it should be possible to monitor the coating surface process of large-area substrates, and if necessary, carry out remedial work on the process parameters
Dr. Glendon Swarthout
No full textHosted by Roger M. Busfield, MSU Assistant Professor of Speech and Theater, Meet the Author is designed to introduce a general audience to a contemporary author and their work through in-depth interviews. This episode features a conversation between Dr. Glendon Swarthout, prolific author and English professor at MSU, and assistant professors Sam S. Baskett and Theodore B. Strandness
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