Absolute Conversion Research Articles

Improvement of conversion efficiency of multicrystalline silicon solar cells by incorporating reactive ion etching texturing

The reactive ion etching in combination with acidic etching (acidic+RIE) is applied to form the front surface texturing of 156×156mm2 multicrystalline silicon (mc-Si) wafers in order to improve the cell efficiency. The scanning electron microscope (SEM) analyses indicate that the RIE process produces dense nanoscale ridge-like structures based on the acidic textured surfaces, and these structures generate an excellent antireflection effect. The matching processes including the post-cleaning, the phosphorus diffusion, and the deposition of silicon nitride (SiNX) antireflection coating are optimized. The acidic+RIE textured surfaces in combination with high sheet resistance emitters result in a remarkable enhancement in short wavelength response and then improve the short circuit current density (JSC) significantly. The absolute conversion efficiency of acidic+RIE textured solar cells is improved 0.51% on average compared to the acidic textured solar cells in mass production, and a maximum full-area cell efficiency of 18.49% is achieved on the mc-Si solar cell with a conventional cell structure.

Monte Carlo modeling of HD120 multileaf collimator on Varian TrueBeam linear accelerator for verification of 6X and 6X FFF VMAT SABR treatment plans.

A Monte Carlo (MC) validation of the vendor‐supplied Varian TrueBeam 6 MV flattened (6X) phase‐space file and the first implementation of the Siebers‐Keall MC MLC model as applied to the HD120 MLC (for 6X flat and 6X flattening filterfree (6X FFF) beams) are described. The MC model is validated in the context of VMAT patient‐specific quality assurance. The Monte Carlo commissioning process involves: 1) validating the calculated open‐field percentage depth doses (PDDs), profiles, and output factors (OF), 2) adapting the Siebers‐Keall MLC model to match the new HD120‐MLC geometry and material composition, 3) determining the absolute dose conversion factor for the MC calculation, and 4) validating this entire linac/MLC in the context of dose calculation verification for clinical VMAT plans. MC PDDs for the 6X beams agree with the measured data to within 2.0% for field sizes ranging from 2 × 2 to 40 × 40 cm2. Measured and MC profiles show agreement in the 50% field width and the 80%‐20% penumbra region to within 1.3 mm for all square field sizes. MC OFs for the 2 to 40 cm2 square fields agree with measurement to within 1.6%. Verification of VMAT SABR lung, liver, and vertebra plans demonstrate that measured and MC ion chamber doses agree within 0.6% for the 6X beam and within 2.0% for the 6X FFF beam. A 3D gamma factor analysis demonstrates that for the 6X beam, > 99% of voxels meet the pass criteria (3%/3 mm). For the 6X FFF beam, > 94% of voxels meet this criteria. The TrueBeam accelerator delivering 6X and 6X FFF beams with the HD120 MLC can be modeled in Monte Carlo to provide an independent 3D dose calculation for clinical VMAT plans. This quality assurance tool has been used clinically to verify over 140 6X and 16 6X FFF TrueBeam treatment plans.PACS number: 87.55.K‐

Causality between liquidity management and profitability: evidence from Indian CPSEs

This study comprehensively excavates the general relationship and causality between liquidity management and corporate profitability for Indian CPSEs (central public sector enterprises). Liquidity indices like current ratio, liquid ratio, absolute liquid ratio and cash conversion cycle are taken as explanatory variables, whereas, age of creditors, age of debtors, age of inventory and the natural logarithm of sales are taken as control variables. Profitability is measured in terms of return on total assets. The sample size is restricted to 48 Indian CPSEs listed on the National Stock Exchange (NSE) and Bombay Stock Exchange (BSE) of India and the secondary data for analysis is retrieved from CMIE (Centre for Monitoring Indian Economy) for a ten-year period from 2002–2003 to 2011–2012. Statistical and econometric tools like, descriptive statistics, unit root test, fixed effects regression model and Granger causality test are employed in the study. Granger causality test suggests the evidence of feedback causality running between current ratio, liquid ratio, absolute liquid ratio and cash conversion cycle with return on total assets, while, unidirectional causality is found to be running from firms’ size to return on total assets.

Carbon fiber/Co9S8 nanotube arrays hybrid structures for flexible quantum dot-sensitized solar cells

Recently, hybrid carbon materials and inorganic nanocrystals have received an intensive amount of attention and have opened up an exciting new field in the design and fabrication of high-performance catalysts. Here we present a novel kind of hybrid counter electrode (CE) consisting of a carbon fiber (CF) and Co9S8 nanotube arrays (NTs) for fiber-shaped flexible quantum dot-sensitized solar cells (QDSSCs). The growth mechanisms of Co(CO3)0.35Cl0.20(OH)1.10 nanowire arrays (NWs) on the CFs were discussed, and the catalytic activity of the CF, Pt and Co9S8/CF hybrid structure (Co9S8@CF) were elucidated systematically as well. An absolute energy conversion efficiency of 3.79% has been demonstrated under 100 mWcm(-2) AM1.5 illumination by using Co9S8@CF as a CE. This work not only demonstrates an innovative approach for growing cobalt sulfide NTs on flexible substrates that can be applied in flexible devices for energy harvesting and storage, but also provides a kind of hybrid structure and high-efficiency CE for QDSSCs.

SiO2Antireflection Coatings Fabricated by Electron-Beam Evaporation for Black Monocrystalline Silicon Solar Cells

In this work we prepared double-layer antireflection coatings (DARC) by using the SiO2/SiNx:H heterostructure design. SiO2thin films were deposited by electron-beam evaporation on the conventional solar cell with SiNx:H single-layer antireflection coatings (SARC), while to avoid the coverage of SiO2on the front side busbars, a steel mask was utilized as the shelter. The thickness of the SiNx:H as bottom layer was fixed at 80 nm, and the varied thicknesses of the SiO2as top layer were 105 nm and 122 nm. The results show that the SiO2/SiNx:H DARC have a much lower reflectance and higher external quantum efficiency (EQE) in short wavelengths compared with the SiNx:H SARC. A higher energy conversion efficiency of 17.80% was obtained for solar cells with SiO2(105 nm)/SiNx:H (80 nm) DARC, an absolute conversion efficiency increase of 0.32% compared with the conventional single SiNx:H-coated cells.

Sodium-doped Mo back contacts for Cu(In,Ga)Se2 solar cells on Ti foils: Growth, morphology, and sodium diffusion

Sodium addition is necessary to reach high efficiencies with Cu(In,Ga)Se2 (CIGS) solar cells on metallic substrates. This can be achieved using DC-sputtered multilayer Mo back contacts including a sodium-doped layer (Mo:Na). In this study, 450 nm-thick Mo:Na layers were sputter-deposited on Ti foils using a working pressure ranging from 3.4 mTorr to 30 mTorr, and capped with 100 nm-thick, dense, pure Mo layers. The deposition pressure of the Mo:Na layers strongly affected their electrical resistance, optical reflectance, morphology, and crystal quality. The top Mo layer allowed controlling the electrical and optical properties of the back contact, but its own morphology was affected by the structure of the underlying Mo:Na layer. The Na concentration in the CIGS layer varied as a function of the deposition pressure of the Mo:Na layer, inducing changes in the absorber grain size and Ga distribution, as well as in the carrier density. Absolute conversion efficiency improvements over 3% were obtained using the sodium-doped back contacts on Ti foils, leading to a performance which was equivalent to the soda-lime glass reference.

Oxidative stress, uptake and bioconversion of 5-fluorouracil in algae

Impact of cytostatic drug 5-fluorouracil (FU) and its metabolite 2-fluoro-3-alanine (FA) on green alga Scenedesmus quadricauda was studied. FA elevated fluorescence signal of reactive oxygen species (ROS) more pronouncedly than FU at 1 and 10μM doses while both ROS and reactive nitrogen species (RNS/NO) increased more expressively in 100μM FU treatment. Cellular damage staining (Acridine Orange and Calcofluor White) did no reveal substantial difference between FU and FA. Majority of free amino acids including proline was unaffected after 24h of exposure. FA depleted ascorbate peroxidase activity more than FU therefore ascorbate content (AsA) was less affected while FU stimulated glutathione reductase activity less than FA and therefore glutathione (GSH) was more depleted. Both compounds accumulated concentration-dependently with higher absolute FA amounts but FU conversion to FA was also detected. We subsequently influenced 100μM FU- and FA-induced changes using known ROS (DTT – dithiothreitol) and RNS/NO (SNP – sodium nitroprusside and PTIO – 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) modulators and results showed that PTIO depleted NO and elevated ROS while the opposite was found after SNP and DTT addition. Changes of lipid peroxidation (using BODIPY staining) confirmed that FU and FA toxicity is related to alteration of ROS/RNS balance.

Closed circuit desalination series no. 8: record saving of RO energy by SWRO-CCD without need of energy recovery

A theoretical model is developed for comparing reverse osmosis (RO) energy and permeates quality of closed of circuit desalination (CCD) and conventional plug flew desalination (PFD) under the same conditions. The application of the theoretical model is illustrated by a comparison between a CCD unit with two modules each of four elements and a single module conventional PFD unit with eight elements in the context of ocean water (3.5%) desalination with 50% recovery at 25°C under average flux of 13 LMH and 85% efficiency of feed pressurizing pumps using the same membrane elements (SWC6). This model analysis reveals savings of RO energy by CCD compared with conventional PFD as function of its absolute energy conversion (AEC) efficiency (in bracket) as followed: 9.8% (95%), 13.4% (90%), 17.2% (85%), 20.6% (80%), 23.8% (75%), and 28.7% (70%). Most large and modern conventional seawater RO plants operate with AEC efficiency in the range of 70–80% and therefore, the actual RO energy saved by CCD compared with such conventional techniques is found in the respective range of 28.7–20.6%. Despite the large difference in RO energy revealed by the model analysis between the compared techniques, both produce about the same quality permeates. CCD is a continuously staged and pressure-boosted consecutive sequential technology which operates with near AEC efficiency without need for energy recovery (ER) from brine, and the low RO energy requirements by this technique manifest the average diagonal sequential pressure rise as function of increased sequential recovery under conditions of fixed flow rates of pressurized feed and permeate. According to the model analysis, CCD of ocean water (3.5%) at 13 LMH with 50% recovery proceeds with 1.625 kWh/m3 compared with 1.962 kWh/m3 by conventional techniques with AEC efficiency of 85%. The model analysis energy of 1.625 kWh/m3 for ocean water (3.5%) CCD at 13 LMH with 50% recovery agrees with extrapolated energy for ocean water (1.60–1.70 kWh/m3) from experimental results (2.0–2.1 kWh/m3) received for the Mediterranean water (4.1%) under the same conditions. A pressure-volume work model for high pressure pump (HP) (85% eff.) in CCD revealed under infinitesimally small permeation of near zero flux conditions the theoretical minimum energies 1.40 and 1.25 kWh/m3 for the Mediterranean (4.1%) and ocean (3.5%) water, respectively. Extrapolation of experimental CCD energies (HP + CP) to near zero flux revealed 1.44 and 1.29 kWh/m3 for the Mediterranean and ocean water, respectively. The difference between the extrapolated (HP + CP) and theoretical minimum (HP) revealed the minor circulation pump (CP) energy contributions 0.04 and 0.05 kWh/m3 in CCD of the Mediterranean (2.78%) and ocean (3.87%) water sources, respectively.

EPOXI instrument calibration

NASA’s EPOXI mission used the Deep Impact (DI) Flyby spacecraft to deliver a payload of three scientific instruments, two visible cameras and an IR spectrometer, to a close flyby of Comet 103P/Hartley 2 in November 2010. Interpretation of the scientific measurements made using these instruments depends on accurate calibration of the instruments’ performance. Updates to the instrument calibrations achieved during the Deep Impact primary mission and results of continued monitoring of their performance during EPOXI are reported here. The instruments’ performance has remained remarkably stable over the nearly 7years of flight. Significant improvements in the understanding and calibration of the IR spectrometer response non-linearity, time-varying background level, flat field, wavelength map, and absolute spectral response have been achieved. Techniques for reducing some semi-coherent horizontal noise stripes in the visible cameras’ readouts were developed, and some adjustments have been made to their absolute radiometric conversion constants. The data processing pipeline has been updated to incorporate the improvements in the instrument calibrations.

Reduction in Operating Temperature of 25 Series-Connected 820X Concentrator Photovoltaic Module

Under concentration conditions, it is important to manage the operating temperature of a concentrator photovoltaic (CPV) module, because a high-density solar energy enters into the solar cell. We measured the receiver temperature of the CPV module and evaluated the relationship between the temperature and output of the CPV module. 25 series-connected 820X CPV modules with 2- and 4-mm-thick back chassises were fabricated. In the case of a CPV module with a 4-mm-thick back chassis, the receiver temperature was markedly reduced owing to the effective thermal diffusion of the thicker chassis. The absolute conversion efficiency of the CPV module with the 4-mm-thick back chassis was 1.5% higher than that of the module with the 2-mm-thick back chassis. Moreover, we developed a thermal transfer model of the CPV module and calculated the thermal distribution in the CPV module using a thermal transfer simulator.

Single-Crystalline Silicon Solar Cell with Selective Emitter Formed by Screen Printing and Chemical Etching Method: A Feasibility Study

A new method for fabricating crystalline silicon solar cells with selective emitters is presented. In this method, shallow trenches corresponding to metal contact area are first formed by screen printing and chemical etching, followed by heavy doping over the whole front surface of the silicon wafer. After a polymer mask is pasted by aligned screen-printing to cover the shallow trenches, the silicon wafer is etched such that the heavy doping remains at the shallow trench area, while other areas become lightly doped. With the presented method, two screening printing steps are required for obtaining a selective emitter structure on a solar wafer. Compared with existing etch-back methods, the presented one is believed to be able to easily conform with present industrial process. Experimental results show that optical responses at the short and long wavelengths were both improved by applying the proposed selective emitter technique to fabricate solar cells with an a-Si:H film deposited on the back surface. The selective emitter cell with a-Si:H back surface deposition had improvements of 1.66 mA/cm2and 1.23% absolute inJscand conversion efficiency, respectively, compared to the reference cell that had a homogeneous emitter and no a-Si:H on the back surface.

Fluorescence of nitrogen and air

Electron beams with 12 keV particle energy were used to excite nitrogen and air. Light emission has been studied using two types of optical spectrometers and a calibrated silicon photo diode. The relative intensities of the nitrogen emission bands in air have been measured and compared with data from the literature. The intensity ratio of the v=0 to 0 emission of nitrogen at 337 nm in the second positive system between pure nitrogen and air was determined to 12.9 ± 0.6 for 800 hPa total pressure for the best gas purity achieved in the experiments. Potential underlying gas kinetic processes are discussed. A measurement of the absolute conversion efficiency of electron beam power into light in the 337 nm band of nitrogen is presented. Converting the result into the corresponding value for dry air leads to a value of (6.1 ± 0.5) 337 nm photons emitted per MeV electron beam energy deposited in air at 1000 hPa and room temperature. The corresponding value for 800 hPa is (8.1 ± 0.8)/MeV.

Evaluation and Optimization of Grid Patterns of Silicon Solar Cells by Diode and Series Resistance Model

Series resistance in solar cell is known to be one of the key factors which need to be optimized, especially through the design of the front pattern. This paper is the utilization of the improved diode and series resistance model to represent the solar cell. The results show: three buses are suitable for high square resistance and fine grid line. Plating technology can improve the absolute conversion efficiency over 17%. In addition, 71 fingers for three buses and 76 fingers for two buses were select in production. It is imagined that the proposed model is very useful for PV professionals who require simple, fast and accurate PV model to design their cells.

Simultaneous enhanced photon capture and carrier generation in Si solar cells using Ge quantum dot photonic nanocrystals

We propose a novel solar cell structure with photonic nanocrystals coupled to quantum dots (QDs) for advanced management of photons and carriers. The photonic nanocrystals at the surface create an extra interaction between the photons and the QDs, which promotes light trapping. Photo-generated carriers can be efficiently transported by preparing vertically aligned QDs with electronic coupling. Implementation of the proposed structure was realized in crystalline Si solar cells with Ge QDs by development of a simple and practical formation method based on a wet chemical process without any lithography techniques. The wet process utilizes a periodically modulated etching rate induced by self-organized Ge QDs. The effectiveness of the proposed solar cell was demonstrated by the marked increase of the absolute conversion efficiency when compared with the control crystalline Si solar cells. It is found that light trapping by the photonic nanocrystals has a larger contribution to the efficiency improvement than the contributions from the carrier transport of the vertically aligned QDs.

Rectangular Bunched Rutile TiO2 Nanorod Arrays Grown on Carbon Fiber for Dye-Sensitized Solar Cells

Because of their special application in photovoltaics, the growth of one-dimensional single-crystalline TiO(2) nanostructures on a flexible substrate is receiving intensive attention. Here we present a study of rectangular bunched TiO(2) nanorod (NR) arrays grown on carbon fibers (CFs) from titanium by a "dissolve and grow" method. After a corrosion process in a strong acid solution, every single nanorod is etched into a number of small nanowires. Tube-shaped dye-sensitized solar cells are fabricated by using etched TiO(2) NRs-coated CFs as the photoanode. An absolute energy conversion efficiency of 1.28% has been demonstrated under 100 mW cm(-2) AM 1.5 illumination. This work demonstrates an innovative method for growing bunched TiO(2) NRs on flexible substrates that can be applied in flexible devices for energy harvesting and storage.

Lunar X-ray fluorescence observations by the Chandrayaan-1 X-ray Spectrometer (C1XS): Results from the nearside southern highlands

The Chandrayaan-1 X-ray Spectrometer (C1XS) flown on-board the first Indian lunar mission Chandrayaan-1, measured X-ray fluorescence spectra during several episodes of solar flares during its operational period of ∼9 months. The accompanying X-ray Solar Monitor (XSM) provided simultaneous spectra of solar X-rays incident on the Moon which are essential to derive elemental chemistry. In this paper, we present the surface abundances of Mg, Al, Si, Ca and Fe, derived from C1XS data for a highland region on the southern nearside of the Moon. Analysis techniques are described in detail including absolute X-ray line flux derivation and conversion into elemental abundance. The results are consistent with a composition rich in plagioclase with a slight mafic mineral enhancement and a Ca/Al ratio that is significantly lower than measured in lunar returned samples. We suggest various possible scenarios to explain the deviations.

Alliinase from Ensifer adhaerens and Its Use for Generation of Fungicidal Activity.

A bacterium Ensifer adhaerens FERM P-19486 with the ability of alliinase production was isolated from a soil sample. The enzyme was purified for characterization of its general properties and evaluation of its application in on-site production of allicin-dependent fungicidal activity. The bacterial alliinase was purified 300-fold from a cell-free extract, giving rise to a homogenous protein band on polyacrylamide gel electrophoresis. The bacterial alliinase (96 kDa) consisted of two identical subunits (48 kDa), and was most active at 60°C and at pH 8.0. The enzyme stoichiometrically converted (-)-alliin ((-)-S-allyl-L-cysteine sulfoxide) to form allicin, pyruvic acid, and ammonia more selectively than (+)-alliin, a naturally occurring substrate for plant alliinase ever known. The C-S lyase activity was also detected with this bacterial enzyme when S-alkyl-L-cysteine was used as a substrate, though such a lyase activity is absolutely absent in alliinase of plant origin. The enzyme generated a fungicidal activity against Saccharomyces cerevisiae in a time- and a dose-dependent fashion using alliin as a stable precursor. Alliinase of Ensifer adhaerens FERM P-19486 is the enzyme with a novel type of substrate specificity, and thus considered to be beneficial when used in combination with garlic enzyme with respect to absolute conversion of (±)-alliin to allicin.

Elastic Cross Sections for Electron Collisions with Molecules Relevant to Plasma Processing

Absolute electron-impact cross sections for molecular targets, including their radicals, are important in developing plasma reactors and testing various plasma processing gases. Low-energy electron collision data for these gases are sparse and only the limited cross section data are available. In this report, elastic cross sections for electron-polyatomic molecule collisions are compiled and reviewed for 17molecules relevant to plasma processing. Elastic cross sections are essential for the absolute scale conversion of inelastic cross sections, as well as for testing computational methods. Data are collected and reviewed for elastic differential, integral, and momentum transfer cross sections and, for each molecule, the recommended values of the cross section are presented. The literature has been surveyed through early 2010.

Enzyme-Based Hybrid Macroporous Foams as Highly Efficient Biocatalysts Obtained through Integrative Chemistry

Integrative chemistry-based rational design has been used to synthesize the first lipase [C-CRl]@Glymo-Si(HIPE) and [C-TAl]@Glymo-Si(HIPE) hybrid macrocellular biocatalysts, where immobilization of crude enzymes is optimized, while circumventing the reactants’ low kinetic diffusion, by the use of silica macroporous hosts. As a direct consequence, these new hybrid biocatalysts display unprecedented cycling catalysis performance, as demonstrated by the syntheses of butyloleate ester (used as biodiesel lubricant), hydrolysis of linoleic-glycero ester derivatives (end products used for detergent and soap generations), and trans-esterification (reaction involved in the synthesis of low viscosity biodiesel). Considering that the catalytic performances are given in terms of absolute conversion percentage and not just relative enzyme activity, the enzyme@Glymo-Si(HIPE) hybrid macrocellular biocatalysts presented in this study display unprecedented high yield cycling catalysis performances, where turnover numbers ...

Selective emitter solar cell formation by NH3 plasma nitridation and single diffusion

A new and simple process for fabricating a selective emitter solar cell has been proposed. Lightly and heavily doped emitters could be concurrently formed after a single POCl3 diffusion step through the selective formation of SiNx, which serves as the diffusion barrier and can be grown by NH3 plasma nitridation of the Si surface. The desired phosphorus depth profile for the lightly and heavily doped region verifies the eligibility of this process. From the electrical characterization, the selective emitter solar cell fabricated by this process manifests a higher absolute conversion efficiency than a conventional one by 0.5%. It is the enhanced response to the short wavelength light and the reduced surface recombination that causes the considerable improvement in conversion efficiency which is beneficial to further hold the competitive advantage for solar cell manufacturers. Most importantly, the proposed process can be fully integrated into the conventional solar cell process in a mass-production laboratory.