Light Harvesting Schemes for High Efficiency Thin Film Silicon Solar Cells

In Thin Film Silicon (TF-Si) solar cells light harvesting schemes must guarantee an efficient light trapping in the thin absorber layers without decreasing the silicon layers quality and consecutively the p-i-n diodes electrical performance. TF-Si solar cells resilience to the substrate roughness is reported to be possibly improved through optimizations of the cell design and of the silicon deposition processes. By further tailoring the superstrate texture, amorphous silicon / microcrystalline silicon (a-Si:H/mu c-Si:H) tandem solar cells with an initial efficiency up to 13.7 % and a stabilized efficiency up to 11.8 % are demonstrated on single-scale textured superstrates. An alternative approach combining large and smooth features nanoimprinted onto a transparent lacquer with small and sharp textures from as-grown LPCVD ZnO is then shown to have a high potential for further increasing TF-Si devices efficiency. First results demonstrate up to 14.1 % initial efficiency for a TF-Si tandem solar cell

Normalizing Videos of Anterior Eye Segment Surgeries

International audienceAnterior eye segment surgeries are usually video-recorded. If we are able to efficiently analyze surgical videos in real-time, new decision support tools will emerge. The main anatomical landmarks in these videos are the pupil boundaries and the limbus, but segmenting them is challenging due to the variety of colors and textures in the pupil, the iris, the sclera and the lids. In this paper, we present a solution to reliably normalize the center and the scale in videos, without explicitly segmenting these landmarks. First, a robust solution to track the pupil center is presented: it uses the fact that the pupil boundaries, the limbus and the sclera / lid interface are concentric. Second, a solution to estimate the zoom level is presented: it relies on the illumination pattern reflected on the cornea. The proposed solution was assessed in a dataset of 186 real-live cataract surgery videos. The distance between the true and estimated pupil centers was equal to 8.0+/-6.9% of the limbus radius. The correlation between the estimated zoom level and the true limbus size in images was high: R = 0.83

Indexing of cataract surgery video by content based video retrieval (CBVR)

International audienceMany surgical computer-aided projects ( CAD ) have emerged in recent years, but none interested in cataract surgery . The aim of our study was to develop a method able to recognize in real time the video stream, identified surgical activities and classify them in a database. We propose to analyze the video stream using a new method describing different levels of granularity : procedure, phases, steps and activities

Automated Surgical Step Recognition in Normalized Cataract Surgery Videos

International audienceHuge amounts of surgical data are recorded during video-monitored surgery. Content-based video retrieval systems intent to reuse those data for computer-aided surgery. In this paper, we focus on real-time recognition of cataract surgery steps: the goal is to retrieve from a database surgery videos that were recorded during the same surgery step. The proposed system relies on motion features for video character- ization. Motion features are usually impacted by eye motion or zoom level variations, which are not necessarily relevant for surgery step recognition. Those problems certainly limit the performance of the retrieval system. We therefore propose to refine motion feature extraction by applying pre-processing steps based on a novel pupil center and scale tracking method. Those pre-processing steps are evaluated for two different motion features. In this paper, a similarity measure adapted from Piciarelli's video surveillance system is evaluated for the first time in a surgery dataset. This similarity measure provides good results and for both motion features, the proposed pre- processing steps improved the retrieval performance of the system significantly

Real-time analysis of cataract surgery videos using statistical models

International audienceThe automatic analysis of the surgical process, from videos recorded during surgeries, could be very useful to surgeons, both for training and for acquiring new techniques. The training process could be optimized by automatically providing some targeted recommendations or warnings, similar to the expert surgeon’s guidance. In this paper, we propose to reuse videos recorded and stored during cataract surgeries to perform the analysis. The proposed system allows to automatically recognize, in real time, what the surgeon is doing: what surgical phase or, more precisely, what surgical step he or she is performing. This recognition relies on the inference of a multilevel statistical model which uses 1) the conditional relations between levels of description (steps and phases) and 2) the temporal relations among steps and among phases. The model accepts two types of inputs: 1) the presence of surgical tools, manually provided by the surgeons, or 2) motion in videos, automatically analyzed through the Content Based Video retrieval (CBVR) paradigm. Different data-driven statistical models are evaluated in this paper. For this project, a dataset of 30 cataract surgery videos was collected at Brest University hospital. The system was evaluated in terms of area under the ROC curve. Promising results were obtained using either the presence of surgical tools (Az = 0.983) or motion analysis (Az = 0.759). The generality of the method allows to adapt it to other kinds of surgeries. The proposed solution could be used in a computer assisted surgery tool to support surgeons during the surgery. © 2017, Springer Science+Business Media New York

Silicon oxide buffer layer at the p-i interface in amorphous and microcrystalline silicon solar cells

The use of intrinsic silicon oxide as a buffer layer at the p-i interface of thin-film silicon solar cells is shown to provide significant advantages. For microcrystalline silicon solar cells, when associated with highly crystalline i-layers deposited at high rates, all electrical parameters are improved. Larger efficiency gains are achieved with substrates of increased roughness. For cells with an improved i-layer material quality, there is mainly a gain in short-circuit current density. An improvement in carrier collection in the blue region of the spectrum is systematically observed on all the cells. The presence of a silicon oxide buffer layer also promotes the nucleation of the subsequent intrinsic microcrystalline silicon layer. In amorphous silicon solar cells, the silicon oxide buffer layer is proven to act as an efficient barrier to boron cross-contamination, eliminating the need for additional processing steps (e.g. water vapor flush), while providing a wide bandgap material at the interface. The implementation of silicon oxide buffer layers for both types of cells thus provides a decisive improvement, as it allows extremely fast deposition of the full p-i-n stack of layers of the cell in a single-chamber configuration while providing a high-quality substrate-resilient p-i interface. (C) 2013 Elsevier B.V. All rights reserved

9.4% Efficient Amorphous Silicon Solar Cell on High Aspect-Ratio Glass Microcones

High aspect-ratio three-dimensional (3D) a-Si:H solar cells have been fabricated to enhance a light absorption path while maintaining a short carrier collection length. Substantial efficiency enhancement in 3D solar cells was achieved due to the boost in JSC with no degradation of FF which is comparable to FF obtained from 2D solar cells

Permanent dichroic coloring of surfaces by laser-induced formation of chain-like self-organized silver nanoparticles within crystalline titania films.

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Journal of Hydrology

In groundwater management, the determination of the origins of nitrate (NO3–) endmember sources is the first step in improving the management over a hydrogeological catchment. The generally multiple source contamination by nitrate over the karst systems makes it difficult to identify the exact nitrate origins in surface water and groundwater. This work aims to assess nitrate vulnerability of a karst system fed by several karst aquifers. The Toulon karst system offers the opportunity to study the relationships between two multilayered karst aquifers. It shows an increase in mean NO3– concentrations over decades. However, the origins of the NO3– remain unclear. Natural stable isotopic composition of NO3– (δ15N-NO3– and δ18O-NO3–) measurements combined with concentrations were used to identify the origins of nitrogen causing this increase. This information was also integrated into the local hydrogeological situation to improve knowledge of the contamination of both confined and unconfined karst aquifers. δ15N-NO3− and δ18O-NO3− in potential nitrate sources over the hydrogeological catchment were analysed in order to identify the range of values that can be measured in both rivers and groundwater. Over the Toulon Springs catchment, rivers are contaminated with nitrate coming from N synthetic fertilizer mineralized in agriculturalsoils. Most of the springs are also contaminated by this nitrate source, but some record an isotope composition of nitrate coming from sewage effluents. Toulon Springs are only contaminated with nitrate from N synthetic fertilizer mineralized in agricultural soils. Finally, from a hydrogeological point of view, the analysis of δ15N-NO3− and δ18O-NO3− values improves knowledge on the functioning of the study area and shows that the upper Jurassic karst confined aquifer has nitrate of the same origins (sources) as the upper Cretaceous unconfined aquifer. The results here highlight that the lower aquifer can be fed by the Upper Cretaceous unconfined aquifer, contrary to previous belief that the lower aquifer was confined. From a more fundamental standpoint, this work provides a set of parameters adapted for karstic hydrogeological catchment. It lays the foundation for the use of isotope biogeochemistry as a powerful tool for understanding the recharge of drinking water catchments and beyond the efficient management of water quality at the scale of karstic hydrogeological catchment

Light harvesting schemes for high efficiency thin film silicon solar cells

Objectives Patient recall of medical information is usually poor. Healthcare providers can employ affect-oriented (i.e., showing care) or cognition-oriented communication styles (i.e., structuring information) to enhance recall, but research evidence is limited especially among clinical and/or older patient populations. This video-vignette study manipulated provider caring and information structuring to examine effects on recall and trust among cancer patients/survivors. Methods In an online survey, 148 participants (Mage = 62) were randomized to one of four video conditions in a two (standard communication vs. enhanced caring) by two (standard vs. enhanced structuring) design, and completed measures of active recall, recognition, and trust. Results Increased caring or structuring did not enhance active recall or recognition, instead both were higher among younger, female, or highly educated participants. The caring condition induced higher perceived trust in the provider within the whole sample, but trust was significantly correlated with decreased recall (r = −.268) among younger participants. Conclusions Provider caring can strengthen the patient-provider relationship by enhancing trust. Yet, increased trust may impair recall among younger patients. Structuring treatment information did not enhance recall and recognition, but additional research is needed. Practice implications Providers may use additional ways of structuring/organizing information to help enhance recall (e.g., written information)