Manufacturing and analysis of wave-shaped wires for stress-reduced interconnection of silicon solar cells

Der Standardprozess für die Verschaltung von Siliziumsolarzellen ist Löten. Unterschiedliche thermische Ausdehnungskoeffizienten der eingesetzten Materialien erzeugen thermomechanische Spannungen nach dem Lötvorgang. Diese können zu Defekten führen, welche die Ausgangsleistung photovoltaischer Module verringern. In dieser Arbeit wurden thermomechanische Spannungen aufgrund des Lötvorgangs mittels der Finite Elemente Methode analysiert. Die Ergebnisse ermöglichen eine Optimierung des Kontaktmetallisierungslayouts von Solarzellen, sodass Spannungsmaxima reduziert werden können. Außerdem beeinflussen die mechanischen Eigenschaften von zur Verschaltung eingesetzten Kupferzellverbindern thermomechanische Spannungen wesentlich. Deshalb wurden gewellte Drähte eingeführt und deren physikalische Eigenschaften analysiert. Mittels neu entwickelter Umformmethoden wurde eine Reduktion der Pseudo-Dehngrenze von bis zu −88, 5% erreicht. Dies zeigt das Potential gewellter Drähte thermomechanische Spannungen deutlich zu reduzieren. Berechnungen zeigen außerdem, dass durch eine Verschaltung mit gewellten Drähten eine Erhöhung der Modulleistung um bis zu 2,1% möglich ist. Zudem wird das Löten auf Kleinstkontakten ermöglicht und die Biegeverformung bei einseitiger Verschaltung von hocheffizienten Rückkontaktsolarzellen maßgeblich reduziert. Thermische Zyklentests zeigen eine Leistungsdegradation kleiner −3% nach 200 Zyklen und damit vergleichbare Ergebnisse wie Standardverschaltungsansätze.Soldering of copper interconnectors is the standard process for the interconnection of silicon solar cells. Different coefficients of thermal expansion of the used materials cause thermomechanical stress after the soldering process. Thermomechanical stress may induce defects that result in power degradation of photovoltaic modules. In this work, thermomechanical stress caused by the soldering process is examined by finite element analyses. The results reveal how to optimize the metallization layout for reduced stress maxima. In addition, the mechanical properties of copper ribbons or wires used for the interconnection significantly affect thermomechanical stress. For this reason, wave-shaped wires were introduced and their physical properties were analyzed. Using newly developed reshaping methods a pseudo yield limit reduced by up to −88.5% is possible. This indicates the potential of wave-shaped wires for significant stress reduction. Simulations show a maximum power increase of 2.1% when interconnecting solar cells with wave-shaped wires. In addition, wave-shaped wires enable soldering on smallest contacts and the bending deformation of high efficiency back-contact solar cells is significantly reduced. Furthermore, temperature cycling shows a power degradation below −3% after 200 cycles, which is comparable to standard interconnection approaches

Single Molecule DNA Detection with an Atomic Vapor Notch Filter

The detection of single molecules has facilitated many advances in life- and material-sciences. Commonly, it founds on the fluorescence detection of single molecules, which are for example attached to the structures under study. For fluorescence microscopy and sensing the crucial parameters are the collection and detection efficiency, such that photons can be discriminated with low background from a labeled sample. Here we show a scheme for filtering the excitation light in the optical detection of single stranded labeled DNA molecules. We use the narrow-band filtering properties of a hot atomic vapor to filter the excitation light from the emitted fluorescence of a single emitter. The choice of atomic sodium allows for the use of fluorescent dyes, which are common in life-science. This scheme enables efficient photon detection, and a statistical analysis proves an enhancement of the optical signal of more than 15% in a confocal and in a wide-field configuration.Comment: 9 pages, 5 figure

Diffusion properties of single FoF1-ATP synthases in a living bacterium unraveled by localization microscopy

FoF1-ATP synthases in Escherichia coli (E. coli) bacteria are membrane-bound enzymes which use an internal proton-driven rotary double motor to catalyze the synthesis of adenosine triphosphate (ATP). According to the 'chemiosmotic hypothesis', a series of proton pumps generate the necessary pH difference plus an electric potential across the bacterial plasma membrane. These proton pumps are redox-coupled membrane enzymes which are possibly organized in supercomplexes, as shown for the related enzymes in the mitochondrial inner membrane. We report diffusion measurements of single fluorescent FoF1-ATP synthases in living E. coli by localization microscopy and single enzyme tracking to distinguish a monomeric enzyme from a supercomplex-associated form in the bacterial membrane. For quantitative mean square displacement (MSD) analysis, the limited size of the observation area in the membrane with a significant membrane curvature had to be considered. The E. coli cells had a diameter of about 500 nm and a length of about 2 to 3 \mum. Because the surface coordinate system yielded different localization precision, we applied a sliding observation window approach to obtain the diffusion coefficient D = 0.072 \mum2/s of FoF1-ATP synthase in living E. coli cells.Comment: 12 pages, 6 figure

Implementing a 4 Week Balance Protocol to Impact Quality of Life in Cancer Patients

International Journal of Exercise Science 8(2): 145-153, 2015. As a result of various cancer treatments, balance, fall risk, and quality of life (QOL) of cancer survivors are often negatively compromised. There has been no prior research conducted examining balance ability and its association with QOL in cancer patients. The purpose of this study was to investigate whether improved balance will positively influence QOL. Eight female cancer patients (age 55.8 ± 11.8 yrs.) volunteered for an experimental group, and five sex-matched cancer patients (age 64.5 ± 4.6 yrs.) volunteered for a control group. A 4-week balance program, employed twice per week and consisting of 5 different exercises, was utilized with the experimental group participants. Measures of balance and fall risk were obtained using a balance system (Biodex SD 950-440). QOL was assessed by employing the Functional Assessment of Cancer Therapy-General (FACT-G) survey. Alpha level of .05 was used for all statistical analyses. There was no significant relationship between QOL and fall risk (r=.08, p=.790). A two-way ANOVA demonstrated significant group difference in QOL, but not time. More specifically, control group had higher QOL score than did experimental group. A second two-way ANOVA shows no significant difference in fall risk between groups nor time. Due to a lack of improvement in balance from pre- to post-tests, we did not examine an improvement in QOL scores among cancer patients. Further research needs to be completed to more appropriately measure improvements in balance and a longer-term intervention

Die Schiffsbauindustrie in der Meiji-Zeit

Die japanische Schiffsbauindustrie ist im deutschsprachigen Raum weitestgehend unerforscht. Diese Arbeit hat sich das Ziel gesetzt, die strukturellen Rahmenbedingungen der japanischen Schiffsbauindustrie in der Meiji-Zeit sowie die wichtigsten beteiligten Akteure des japanischen Schiffbaus darzustellen. Anhand japanischer Primär- und Sekundärliteratur sowie westlicher Sekundärliteratur wird an das Thema herangegangen und der Fokus der Arbeit liegt insbesondere auf der Entwicklung des privaten Sektors der japanischen Schiffswerften und der japanischen Reedereien. Den wichtigsten Schwerpunkt nehmen hierbei die Gesetze zur Förderung des Schiffbaus und zur Förderung der Schifffahrt ein, deren Bedeutsamkeit hinsichtlich des Schiffbaus erörtert wird

Reduction of Thermomechanical Stress Using Electrically Conductive Adhesives

We compare the thermomechanical stresses in solar cell interconnections based on electrically conductive adhesives (ECA) with soldered joints by using bending experiments and finite element analysis (FEA). Additionally, the influence of an increasing number of busbars is studied. The FEA is validated by measuring the bending of cell strips after cooling down from a single-sided interconnection process. The material parameters are determined by tensile tests, microscopy and nanoindentation. The comparison of ECA and soldering shows that an elastomer with a Young's modulus of below 0.5 GPa is capable of reducing the thermomechanical stress effectively resulting in, approximately, a mean tensile stress in the ECA of 5 MPa, 110 MPa in the ribbon, and a maximum compressive stress in the silicon of 75 MPa. Increasing the number of busbars from three to five leads to a reduction in compressive stresses in the silicon and a slight increase of the peak tensile stress in the busbars

Monitoring single membrane protein dynamics in a liposome manipulated in solution by the ABELtrap

FoF1-ATP synthase is the essential membrane enzyme maintaining the cellular level of adenosine triphosphate (ATP) and comprises two rotary motors. We measure subunit rotation in FoF1-ATP synthase by intramolecular Foerster resonance energy transfer (FRET) between two fluorophores at the rotor and at the stator of the enzyme. Confocal FRET measurements of freely diffusing single enzymes in lipid vesicles are limited to hundreds of milliseconds by the transit times through the laser focus. We evaluate two different methods to trap the enzyme inside the confocal volume in order to extend the observation times. Monte Carlo simulations show that optical tweezers with low laser power are not suitable for lipid vesicles with a diameter of 130 nm. A. E. Cohen (Harvard) and W. E. Moerner (Stanford) have recently developed an Anti-Brownian electrokinetic trap (ABELtrap) which is capable to apparently immobilize single molecules, proteins, viruses or vesicles in solution. Trapping of fluorescent particles is achieved by applying a real time, position-dependent feedback to four electrodes in a microfluidic device. The standard deviation from a given target position in the ABELtrap is smaller than 200 nm. We develop a combination of the ABELtrap with confocal FRET measurements to monitor single membrane enzyme dynamics by FRET for more than 10 seconds in solution.Comment: 12 pages, 10 figure

Coherent electrical readout of defect spins in 4H-SiC by photo-ionization at ambient conditions

Quantum technology relies on proper hardware, enabling coherent quantum state control as well as efficient quantum state readout. In this regard, wide-bandgap semiconductors are an emerging material platform with scalable wafer fabrication methods, hosting several promising spin-active point defects. Conventional readout protocols for such defect spins rely on fluorescence detection and are limited by a low photon collection efficiency. Here, we demonstrate a photo-electrical detection technique for electron spins of silicon vacancy ensembles in the 4H polytype of silicon carbide (SiC). Further, we show coherent spin state control, proving that this electrical readout technique enables detection of coherent spin motion. Our readout works at ambient conditions, while other electrical readout approaches are often limited to low temperatures or high magnetic fields. Considering the excellent maturity of SiC electronics with the outstanding coherence properties of SiC defects the approach presented here holds promises for scalability of future SiC quantum devices