Relative Efficiency Increase Research Articles

Increasing Upconversion by Plasmon Resonance in Metal Nanoparticles—A Combined Simulation Analysis

Upconversion (UC) of subbandgap photons has the potential to increase solar cell efficiencies. In this paper, we first review our recent investigations of silicon solar cell devices with an attached upconverter based on β-NaYF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> :20%Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> . Such devices showed peak external quantum efficiencies of 0.64% under monochromatic excitation at 1523 nm and an irradiance of 2305 Wm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> . Under broad spectrum illumination, an average UC efficiency of 1.07 ± 0.13% in the spectral range from 1460 to 1600 nm was achieved. The measured quantum efficiency corresponds to a relative efficiency increase of 0.014% for the used bifacial silicon solar cell with 16.70% overall efficiency. This increase is too small to make UC relevant in photovoltaics. Therefore, additional means of increasing the UC efficiency are necessary. In this paper, we investigate plasmon resonance in metal nanoparticles in the proximity of the UC material, with the aim of increasing UC efficiency. The local field enhancement by the plasmon resonance positively influences UC efficiency because of the nonlinear nature of UC. Additionally, the metal nanoparticles also influence the transition probabilities in the upconverter. To investigate the effects, we combine different simulation models. We use a rate equation model to describe the UC dynamics in β-NaYF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> :20%Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> . The model considers ground state and excited state absorption, spontaneous and stimulated emission, energy transfer, and multiphonon decay. The rate equation model is coupled with Mie theory calculations of the changed optical field in the proximity of a gold nanoparticle. The changes of the transition rates both for radiative and nonradiative processes are calculated with exact electrodynamic theory. Calculations are performed in high resolution for a 3-D simulation volume. The results suggest that metal nanoparticles can increase UC efficiency.

Novel series connection concept for thin film solar modules

ABSTRACTThe paper introduces a new type of series connection that considerably increases the active area and thus the efficiency of a thin film module by a superior arrangement of the patterning grooves. The new concept is mainly based on pointwise contacts instead of continuous, stripe‐like contacts between adjacent cell stripes combined with a modified arrangement of the isolation grooves. We describe the functionality of the innovative series connection and present a method to calculate the optimal cell stripe geometry for cells based on the new series connection concept. Finally, the applicability of the new concept for a laser‐patterned thin film silicon solar module is demonstrated. The new series connection leads to a relative efficiency increase of approximately 3% compared with the standard series connection for thin film modules. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Efficiency enhancement of silicon solar cells with silicon nanocrystals embedded in PECVD silicon nitride matrix

Anti reflection coatings (ARC), comprising of silicon-rich-nitride (SRN) films embedded with downconverting silicon nanocrystals were integrated into monocrystalline silicon solar cells fabricated using standard semiconductor fabrication techniques, and their effects were studied. Two types of ARC layers, one with single layer SRN film and other with double layer SiOx/SRN were deposited by plasma enhanced chemical vapor deposition (PECVD) during fabrication of silicon solar cells and thermally annealed to precipitate silicon nanocrystals. A relative increase in power conversion efficiency of 15.6% for single layer nanocrystals-embedded-ARC and 22.8% for double layer nanocrystals-embedded-ARC were observed compared to a reference cell.

Performance improvement of plasma actuators using asymmetric high voltage waveforms

An experimental study is conducted on high voltage waveforms used to power plasma actuators. Shapes that present an asymmetry between the two half cycles are investigated by means of induced thrust and velocity measurements. A parametric study is performed based on thrust measurements in order to find the optimum shape within the tested range. An asymmetric waveform which is made as a combination of sinusoidal and square shapes is found to increase produced thrust by almost 30% compared with the conventional sinusoidal waveform. The asymmetric waveform is further analysed using time-resolved particle image velocimetry in order to reveal the forcing mechanism governed by the shape differences. It is shown that the shape of the waveform has a significant effect on the performance of the actuator. Push and pull events occur within the actuation period and their respective strength and duration closely correlates with the shape of the waveform. It is found that the pull event is significantly weakened for the case of the optimized asymmetric waveform in comparison with the sinusoidal shape. This effectively increases the net momentum transfer and an improvement of approximately 40% in maximum induced velocity is achieved compared with sine waveform. Power consumption due to the asymmetric waveform is marginally increased which provides a significant increase in the actuator's relative efficiency.

A universal optical approach to enhancing efficiency of organic-based photovoltaic devices

We report a new optical approach that can be used to enhance light harvesting in many different organic-based photovoltaic cells. A transparent polymer microlens array moulded on the light incident surface increases the light path in the active layer and reduces surface reflection, resulting in a 15–60% relative increase in overall cell efficiency.

Empirical Testing of Balassa-Samuelson Hypothesis with German and UK Data

There are a lot of studies that test Ballasa –Samuelson hypothesis also known as Harrod-BalassaSamuelson effect directly via the effect of productivity, one possible explanation is that PER Capita GDP is not good explanation for productivity (.i.e. Labor productivity) differences; an increase (decrease) in relative efficiency of the distribution sector with respect to foreign countries induces depreciation (appreciation) of the exchange rate. After we obtained the number of co-integrated vectors we continue further to see whether the CV tells us something about the long run relationship into the model, likelihood ratio test of exactly identified restrictions test confirms that constant is insignificant variable therefore we can confirm that there is long-run relationship in which the changes in Exchange rate are positively correlated with the changes of ratio of German Consumer Price Index (CPI) to the UK Retail Price Index (RPI). In order to test for relative PPP to support the theoretical relationship between the variables, restrictions are put on the PPP knowing that PPP and that downward movement in the series indicates increase of UK price level relative to German price level. In each EC model there is an EC mechanism and coefficient on the co integrating vector measures the rate per period at which one of the endogenous variables adjusts. In the first equation the error correction mechanism is highly significant and negative. If the system is out of equilibrium, alteration in the change of the exchange rates will be downward (everything else ceteris paribus) compensating around 68% of the disequilibrium per year. In the second equation error correction mechanism is also highly significant but positive meaning that if the system is in disequilibrium changes of change in the ratio of German CPI relative to UK Retail Price index will rise offsetting 15% of the disequilibrium per year until the equilibrium rate of exchange rate will be achieved. Model implies German Labor productivity to UK Labor productivity ratio doesn’t have significant influence on explaining on relative change on prices not even on theexchange rate contrary to Pugh, Beachil study

Edge Passivation of Si Solar Cells by Omnidirectional Hydrogen Plasma Implantation

Plasma immersion ion implantation of hydrogen with low kinetic energy (1 kV) was used to passivate solar cells to increase efficiency. The plasma sheath encloses the wafer cell and hydrogen ions can be implanted into the entire cell surface. The passivation is omnidirectional, and is particularly effective at the edge surface of the solar cell. The large diffusion length of carriers in Si solar cell is susceptible to edge defects, since the photo-generated carriers can diffuse to the edge surfaces and recombine to degrade the efficiency. Moreover, the dielectric/silicon interface can be effectively passivated due to energetic hydrogen from plasma. For small-area cell, an increase in relative efficiency of 4.4% was obtained after a 90 s plasma immersion ion implantation treatment. Both the external quantum efficiency for 400–500 nm wavelength photons and photoluminescence intensity increase by ∼6% and ∼29% relatively.

Low gap superconducting single photon detectors for infrared sensitivity

The quantum efficiency of NbN and NbTiN superconducting single photon detectors drops with decreasing photon energy. A lower gap material would enable single photon detection deeper in the infrared. We have fabricated a NbSi detector and compare its characteristics with a NbTiN device. NbSi (TC≃2 K) has a smaller superconducting gap than NbTiN or NbN (TC≃15 K). We measure the detection efficiency for a wavelength range from 1100 to 1900 nm. In this range the NbSi detector shows a 10-fold increase in relative efficiency with respect to the NbTiN detector.

LPCVD ZnO-based intermediate reflector for micromorph tandem solar cells

The use of zinc oxide (ZnO) based intermediate reflector (ZIR) in micromorph solar cells using low pressure chemical vapor deposition (LPCVD) was investigated. The influences of deposition temperature and dopant gas concentration on grain size and lateral electrical conductivity measurements are presented. Further ZIR deposition conditions were then directly evaluated in micromorph solar cell devices. Their electrical performances were compared to reference cells and cells incorporating silicon oxide based intermediate reflector. It is shown that both reduced ZIR deposition temperature and increased total flow rate allow for better performing devices with increased shunt resistance, as further supported by lock-in thermography shunt imaging. Relative micromorph efficiency increase of above 7% is shown with thin ZnO layers, along with absence of loss or even small increase of total current in the whole structure compared to cells without intermediate reflector.

Improved photovoltaic effect of polymer solar cells on planarized 2D photonic crystals

We herein advance the application of a two-dimensional (2D) photonic crystal (PC) as a window layer in an efficient polymer solar cell (PSC). The PSC used here consisted of a photovoltaic (PV) layer of poly(3-hexylthiophene): methanofullerene bulk-heterojunction with a planarized 2D PC window layer made of a hexagonal array of columns of SiO 2 nano-rods embedded in a dielectric layer of SiN x . By means of a theoretical simulation of the 2D PCs using a finite-difference time-domain (FDTD) method, it was shown that the path length of the incident light can be increased with a large deflection angle. The experimental results confirmed the simulated results obtained using the 2D PC layer. Furthermore, it was shown that a relative increase in power conversion efficiency (PCE) of about 25% was achieved for the PSC with the 2D PC layer, indicating that this layer induces further photon absorption due to efficient light-harvesting within the PV layer.

Influence of Apolipoprotein (Apo) A-I Structure on Nascent High Density Lipoprotein (HDL) Particle Size Distribution

The principal protein of high density lipoprotein (HDL), apolipoprotein (apo) A-I, in the lipid-free state contains two tertiary structure domains comprising an N-terminal helix bundle and a less organized C-terminal domain. It is not known how the properties of these domains modulate the formation and size distribution of apoA-I-containing nascent HDL particles created by ATP-binding cassette transporter A1 (ABCA1)-mediated efflux of cellular phospholipid and cholesterol. To address this issue, proteins corresponding to the two domains of human apoA-I (residues 1-189 and 190-243) and mouse apoA-I (residues 1-186 and 187-240) together with some human/mouse domain hybrids were examined for their abilities to form HDL particles when incubated with either ABCA1-expressing cells or phospholipid multilamellar vesicles. Incubation of human apoA-I with cells gave rise to two sizes of HDL particles (hydrodynamic diameter, 8 and 10 nm), and removal or disruption of the C-terminal domain eliminated the formation of the smaller particle. Variations in apoA-I domain structure and physical properties exerted similar effects on the rates of formation and sizes of HDL particles created by either spontaneous solubilization of phospholipid multilamellar vesicles or the ABCA1-mediated efflux of cellular lipids. It follows that the sizes of nascent HDL particles are determined at the point at which cellular phospholipid and cholesterol are solubilized by apoA-I; apparently, this is the rate-determining step in the overall ABCA1-mediated cellular lipid efflux process. The stability of the apoA-I N-terminal helix bundle domain and the hydrophobicity of the C-terminal domain are important determinants of both nascent HDL particle size and their rate of formation.

Optimization of the p–i interface properties in thin film microcrystalline silicon solar cell

Hydrogenated microcrystalline silicon (μc-Si:H) has become attractive for use in thin-film silicon solar cells. The external quantum efficiency (EQE) of μc-Si:H solar cells extends up to 1100 nm, which is exploited in tandem solar cells. Properties of p–i interface are critical for performance as it affects carrier collection, which is visible in the blue response. Here, we report how μc-Si:H p- and i-layer material properties influence the p–i interface of μc-Si:H solar cells. The effect of RF PECVD parameters of these layers on the p–i interface was investigated. We find that the blue response of the solar cell is sensitive to the crystallinity of both the p- and i-layers. We demonstrate that transient depletion during i-layer deposition affects the blue response of μc-Si:H solar cell. We obtained a narrow process window for optimal solar-cell performance. At the optimal deposition pressure of 9 mbar and using transient depletion, an EQE at 400 nm of 0.6 was obtained, achieving 16% higher short-circuit current density. Reducing the diborane flow during p-layer deposition yielded 13% relative increase in efficiency.

Silicon oxide based n-doped layer for improved performance of thin film silicon solar cells

We propose the use of n-doped silicon oxide as alternative n-layer in thin film Si p-i-n solar cells. By varying input gas ratios, films with a wide range of optical and electrical properties are obtained. Applying these layers in solar cells, good electrical and optical properties are demonstrated. A relative efficiency increase up to 13.6% has been observed on the cells adopting a simple Ag back contact. A similar spectral response as with the cell with standard n-layer plus ZnO/Ag back contact is obtained. The deposition of a buffer layer at the back contact can therefore be avoided.

Investigations of the contribution of neutrophils to the genotoxicity of respirable quartz particles

Previously we showed that the relative biological efficiency for induced cell killing by the 76-MeV beam used at the Institut Curie Proton Therapy Center in Orsay increased with depth throughout the spread-out Bragg peak (SOBP). To investigate the repair pathways underlying this increase, we used an isogenic human cell model in which individual DNA repair proteins have been depleted, and techniques dedicated to precise measurements of radiation-induced DNA single-strand breaks (SSBs) and double-strand breaks (DSBs).The 3-Gy surviving fractions of HeLa cells individually depleted of Ogg1, XRCC1, and PARP1 (the base excision repair/SSB repair pathway) or of ATM, DNA-PKcs, XRCC4, and Artemis (nonhomologous end-joining pathway) were determined at the 3 positions previously defined in the SOBP. Quantification of incident SSBs and DSBs by the alkaline elution technique and 3-dimensional (3D) immunofluorescence of γ-H2AX foci, respectively, was performed in SQ20 B cells.We showed that the amount of SSBs and DSBs depends directly on the particle fluence and that the increase in relative biological efficiency observed in the distal part of the SOBP is due to a subset of lesions generated under these conditions, leading to cell death via a pathway in which the Artemis protein plays a central role.Because therapies like proton or carbon beams are now being used to treat cancer, it is even more important to dissect the mechanisms implicated in the repair of the lesions generated by these particles. Additionally, alteration of the expression or activity of the Artemis protein could be a novel therapeutic tool before high linear energy transfer irradiation treatment.

Gender earnings differentials in Taiwan: A stochastic frontier approach

We examine Taiwan's male–female earnings gaps over the past three decades in order to assess the progress in assimilating women into the labor market. Two alternative methods of evaluating earnings gaps are employed in this paper: the traditional Oaxaca–Blinder decomposition method and the less well-known method of evaluating labor market efficiency. Men and women's earnings are converging during this period (1978–2003) while at the same time there is little change in the level of gender discrimination measured by the standard Oaxaca–Blinder method. Using the labor market efficiency (stochastic frontier) model we find increases in labor market efficiency over time for both males and females; however, females enjoy a much faster rate of increase in efficiency. We conclude that the relative increase in female efficiency represents a decline in discrimination against females.

On the RF/DSP design for efficiency of OFDM transmitters

In this paper, a system-level RF/digital signal processing (DSP) design approach of power-efficient orthogonal frequency-division multiplexing (OFDM) transmitters is proposed. A DSP-based low-IF architecture, which allows a significant enhancement of their power and spectrum efficiencies, is proposed. The cascade of the peak-to-average power ratio (PAPR) reduction technique, predistortion technique, and the in-phase and quadrature modulation led to impressive improvement in the power efficiency and effective linear output power of the OFDM transmitter. Measurement results carried out on an IEEE 802.11a transmitter designed and built for this experiment are presented in terms of error vector magnitude (EVM), adjacent channel leakage ratio, and power efficiency. The power stage of this transmitter uses a heterojunction bipolar InGaP transistor operating in a deeply class AB. The cascade of the PAPR reduction and baseband predistortion processing modules results in the reduction of the power backoff operation point by approximately 10 dB accompanied by a relative increase in the wireless local area network transmitter power efficiency by roughly 400% while meeting the emission mask spectrum and EVM levels demanded by the 802.11a standard.

Hydrogen passivation of multi-crystalline silicon solar cells

The effects of hydrogen passivation on multi-crystalline silicon (mc-Si) solar cells are reported in this paper. Hydrogen plasma was generated by means of ac glow discharge in a hydrogen atmosphere. Hydrogen passivation was carried out with three different groups of mc-Si solar cells after finishing contacts. The experimental results demonstrated that the photovoltaic performances of the solar cell samples have been improved after hydrogen plasma treatment, with a relative increase in conversion efficiency up to 10.6%. A calculation modelling has been performed to interpret the experimental results using the model for analysis of microelectronic and photonic structures developed at Pennsylvania State University.

Implications of Atmospheric and Climatic Change for Crop Yield and Water Use Efficiency

Yield of water-limited crops is determined by crop water use and by plant water use efficiency, each of which will be affected by the anticipated rise in atmospheric carbon dioxide (CO(2)) concentration and concomitant increase in temperature. At the leaf level, a given proportional increase in CO(2) concentration generally elicits a similar relative increase in transpiration efficiency (ratio of net photosynthesis to transpiration). The increase in transpiration efficiency may result both from an increase in photosynthetic rate and a decrease in stomatal conductance. Feedbacks involved in scaling from leaf to crop constrain the increase in net carbon gain and reduce the anti-transpiration effect of CO(2) enrichment. As a result, the increase in crop water use efficiency at high CO(2) typically is less than 75% of that measured at the leaf level. By accelerating crop development and reducing harvest index, higher temperatures often erode yield benefits of improved water use efficiency at high CO(2). The fraction of available water that is used by crops could increase with CO(2) concentration because of greater root growth and faster canopy closure, but these effects have received scant study. Field experiments indicate that CO(2) enrichment will increase crop water use efficiency mainly by increasing photosynthesis and growth. Yield should be most responsive to CO(2) when temperatures approximate the optimum for crop growth. Elevating CO(2) can ameliorate negative effects of above-optimal temperatures, but temperatures near the upper limit for crops will depress yields irrespective of CO(2) concentration.

Implications of Atmospheric and Climatic Change for Crop Yield and Water Use Efficiency

Yield of water-limited crops is determined by crop water use and by plant water use efficiency, each of which will be affected by the anticipated rise in atmospheric carbon dioxide (CO2) concentration and concomitant increase in temperature. At the leaf level, a given proportional increase in CO2 concentration generally elicits a similar relative increase in transpiration efficiency (ratio of net photosynthesis to transpiration). The increase in transpiration efficiency may result both from an increase in photosynthetic rate and a decrease in stomatal conductance. Feedbacks involved in scaling from leaf to crop constrain the increase in net carbon gain and reduce the anti-transpiration effect of CO2 enrichment. As a result, the increase in crop water use efficiency at high CO2 typically is less than 75% of that measured at the leaf level. By accelerating crop development and reducing harvest index, higher temperatures often erode yield benefits of improved water use efficiency at high CO2 The fraction of available water that is used by crops could increase with CO2 concentration because of greater root growth and faster canopy closure, but these effects have received scant study. Field experiments indicate that CO2 enrichment will increase crop water use efficiency mainly by increasing photosynthesis and growth. Yield should be most responsive to CO2 when temperatures approximate the optimum for crop growth. Elevating CO2 can ameliorate negative effects of above-optimal temperatures, but temperatures near the upper limit for crops will depress yields irrespective of CO2 concentration.

Hydraulic turbine efficiency

A set of empirical equations has been developed which defines the peak efficiency and shape of the efficiency curve for hydraulic turbines as a function of the commissioning date for the unit, rated head, rated flow, runner speed, and runner throat or impulse turbine jet diameter. The equations are based on an analysis of peak efficiency data from 56 Francis, 33 axial-flow, and eight impulse runners dating from 1908 to the present, with runner diameters ranging from just under 0.6 m to almost 9.5 m. The metric specific speeds (nq) ranged from 5.3 to 294. The root mean square error of the calculated peak efficiency for Francis and axial-flow runners was found to be 0.65%. The shape of the efficiency curves was derived from eight Francis, five Kaplan, three propeller, and four impulse turbines. Charts showing the relationship between calculated and actual efficiency curves for these 20 runners are provided. A good match between calculated and measured or guaranteed efficiency was obtained. The equations were also used to determine the relative increase in peak efficiency for new reaction runners installed in existing casings at 22 powerplants, with a root mean square accuracy of 1.0%. The equations can be used to (i) develop efficiency curves for new and old runners; (ii) compare the energy output of alternative types of turbines, where this choice is available; and (iii) calculate the approximate incremental energy benefit from installing a new runner in an existing reaction turbine casing, or onto the shaft of an impulse unit.Key words: hydraulic turbines, turbine renovation, turbine efficiency.