New Real-Time Quantum Efficiency Measurement System: Preprint

This paper describes a newly developed technique for measuring the quantum eficiiency in solar cells in real-time using a unique, electronically controlled, full-spectrum light source

Carrier Selective, Passivated Contacts for High Efficiency Silicon Solar Cells based on Transparent Conducting Oxides

AbstractWe describe the design, fabrication and results of passivated contacts to n-type silicon utilizing thin SiO2 and transparent conducting oxide layers. High temperature silicon dioxide is grown on both surfaces of an n-type wafer to a thickness <50Å, followed by deposition of tin-doped indium oxide (ITO) and a patterned metal contacting layer. As deposited, the thin-film stack has a very high J0,contact, and a non-ohmic, high contact resistance. However, after a forming gas anneal, the passivation quality and the contact resistivity improve significantly. The contacts are characterized by measuring the recombination parameter of the contact (J0,contact) and the specific contact resistivity (ρcontact) using a TLM pattern. The best ITO/SiO2 passivated contact in this study has J0,contact = 92.5 fA/cm2 and ρcontact = 11.5 mOhm-cm2. These values are placed in context with other passivating contacts using an analysis that determines the ultimate efficiency and the optimal area fraction for contacts for a given set of (J0,contact, ρcontact) values. The ITO/SiO2 contacts are found to have a higher J0,contact, but a similar ρcontact compared to the best reported passivated contacts

Characterization of Epitaxial Film Silicon Solar Cells Grown on Seeded Display Glass: Preprint

We report characterizations of epitaxial film crystal silicon (c-Si) solar cells with open-circuit voltages (Voc) above 560 mV. The 2-um absorber cells are grown by low-temperature (&lt;750 degrees C) hot-wire CVD (HWCVD) on Corning EAGLE XG display glass coated with a layer-transferred (LT) Si seed. The high Voc is a result of low-defect epitaxial Si (epi-Si) growth and effective hydrogen passivation of defects. The quality of HWCVD epitaxial growth on seeded glass substrates depends on the crystallographic quality of the seed and the morphology of the epitaxial growth surface. Heterojunction devices consist of glass/c-Si LT seed/ epi n+ Si:P/epi n- Si:P/intrinsic a-Si:H/p+ a-Si:H/ITO. Similar devices grown on electronically 'dead' n+ wafers have given Voc {approx}630 mV and {approx}8% efficiency with no light trapping features. Here we study the effects of the seed surface polish on epi-Si quality, how hydrogenation influences the device character, and the dominant junction transport physics

Proposed Route to Thin Film Crystal Si Using Biaxially Textured Foreign Template Layers

We have developed a new approach to growing photovoltaic-quality crystal silicon (c-Si) films on glass. Other approaches to film c-Si focus on increasing grain size in order to reduce the deleterious effects of grain boundaries. Instead, we have developed an approach to align the silicon grains biaxially (both in and out of plane) so that 1) grain boundaries are "low-angle" and have less effect on the electronic properties of the material and 2) subsequent epitaxial thickening is simplified. They key to our approach is the use of a foreign template layer that can be grown with biaxial texture directly on glass

Junction Transport in Epitaxial Film Silicon Heterojunction Solar Cells: Preprint

We report our progress toward low-temperature HWCVD epitaxial film silicon solar cells on inexpensive seed layers, with a focus on the junction transport physics exhibited by our devices. Heterojunctions of i/p hydrogenated amorphous Si (a-Si) on our n-type epitaxial crystal Si on n++ Si wafers show space-charge-region recombination, tunneling or diffusive transport depending on both epitaxial Si quality and the applied forward voltage

Hydrogenation of Dislocation-Limited Heteroepitaxial Silicon Solar Cells: Preprint

Post-deposition hydrogenation by remote plasma significantly improves performance of heteroepitaxial silicon solar cells. Heteroepitaxial deposition of thin crystal silicon on sapphire for photovoltaics (PV) is an excellent model system for the study and improvement of deposition on inexpensive Al2O3-coated (100) biaxially-textured metal foils. Without hydrogenation, PV conversion efficiencies are less than 1% on our model system. Performance is limited by carrier recombination at electrically active dislocations that result from lattice mismatch, and other defects. We find that low-temperature hydrogenation at 350 degrees C is more effective than hydrogenation at 610 degrees C. In this work, we use measurements such as spectral quantum efficiency, secondary ion mass spectrometry (SIMS), and vibrational Si-H spectroscopies to understand the effects of hydrogenation on the materials and devices. Quantum efficiency increases most at red and green wavelengths, indicating hydrogenation is affecting the bulk more than the surface of the cells. SIMS shows there are 100X more hydrogen atoms in our cells than dangling bonds along dislocations. Yet, Raman spectroscopy indicates that only low temperature hydrogenation creates Si-H bonds; trapped hydrogen does not stably passivate dangling-bond recombination sites at high temperatures

A randomized, controlled trial of Veriset&trade; hemostatic patch in halting cardiovascular bleeding

David Glineur,1 Marc Hendrikx,2 Dainis Krievins,3 Peteris Stradins,3 Bernhard Voss,4 Thomas Waldow,5 Luc Haenen,6 Martin Oberhoffer,7 Caroline M Ritchie8 1Saint Luc Cliniques Universitaires, Brussels, Belgium; 2Faculty of Medicine and Life Sciences, Jessa Hospital, Hasselt University, Hasselt, Belgium; 3Pauls Stradins Clinical University Hospital, Riga, Latvia; 4German Heart Center Munich, Department of Cardiovascular Surgery, Technische Universit&auml;t M&uuml;nchen, Munich, Germany; 5Heart Center Dresden GmbH, University Hospital Dresden, Dresden, Germany; 6Imelda Hospital, Bonheiden, Belgium; 7Asklepios Klinik St. Georg, Herzchirurgische Abteilung, Hamburg, Germany; 8Covidien, Medical Affairs, Bedford, MA, USA Background: Obtaining hemostasis during cardiovascular procedures can be a challenge, particularly around areas with a complex geometry or that are difficult to access. While several topical hemostats are currently on the market, most have caveats that limit their use in certain clinical scenarios such as pulsatile arterial bleeding. The aim of this study was to assess the effectiveness and safety of Veriset&trade; hemostatic patch in treating cardiovascular bleeding.Methods: Patients (N=90) scheduled for cardiac or vascular surgery at 12 European institutions were randomized 1:1 to treatment with either Veriset&trade; hemostatic patch (investigational device) or TachoSil&reg; (control). After application of the hemostat, according to manufacturer instructions for use, time to hemostasis was monitored. Follow-up occurred up to 90 days post-surgery. Results: Median time to hemostasis was 1.5 min with Veriset&trade; hemostatic patch, compared to 3.0 min with TachoSil&reg; (p&lt;0.0001). Serious adverse events within 30 days post-surgery were experienced by 12/44 (27.3%) patients treated with Veriset&trade; hemostatic patch and 10/45 (22.2%) in the TachoSil&reg; group (p=0.6295). None of these adverse events were device-related, and no reoperations for bleeding were required within 5 days post-surgery in either treatment group. Conclusion: This study reinforces the difference in minimum recommended application time between Veriset&trade; hemostatic patch and TachoSil&reg; (30 s versus 3 min respectively). When compared directly at 3 min, Veriset&trade; displayed no significant difference, showing similar hemostasis and safety profiles on the cardiovascular bleeding sites included in this study. Keywords: surgical bleeding, cardiac surgery, aortic valve replacement, CAB

Charge carrier transport mechanisms of passivating contacts studied by temperature-dependent J-V measurements

The charge carrier transport mechanism of passivating contacts which feature an ultra-thin oxide layer is investigated by studying temperature-dependent current-voltage characteristics. 4-Terminal dark J-V measurements at low temperatures reveal non-linear J-V characteristics of passivating contacts with a homogeneously grown silicon oxide, which result in an exponential increase in contact resistance towards lower temperature. The attempt to describe the R(T) characteristic solely by thermionic emission of charge carriers across an energy barrier leads to a significant underestimation of the resistance by several orders of magnitude. However, the data can be described properly with the metal-insulator-semiconductor (MIS) theory if tunneling of charge carriers through the silicon oxide layer is taken into account. Furthermore, temperature-dependent light J-V characteristics of solar cells featuring passivating contacts at the rear revealed a FF drop at T < 205 K, which is near the onset temperature of the exponential increase in contact resistivity