Application of an improved band-gap narrowing model to the numerical simulation of recombination properties of phosphorus-doped silicon emitters

The commonly used band-gap narrowing (BGN) models for crystalline silicon do not describe heavily doped emitters with desirable precision. One of the reasons for this is that the applied BGN models were empirically derived from measurements assuming Boltzmann statistics. We apply a new BGN model derived by Schenk from quantum mechanical principles and demonstrate that carrier degeneracy and the new BGN model both substantially affect the electron–hole product within the emitter region. Simulated saturation current densities of heavily phosphorus-doped emitters, calculated with the new BGN model, are lower than results obtained with the widely used empirical BGN model of del Alamo.     

Numerical quantification and minimization of perimeter losses in high-efficiency silicon solar cells

This paper presents a quantitative analysis of perimeter losses in high-efficiency silicon solar cells. A new method of numerical modelling is used, which provides the means to simulate a full-sized solar cell, including its perimeter region. We analyse the reduction in efficiency due to perimeter losses as a function of the distance between the active cell area and the cut edge. It is shown how the optimum distance depends on whether the cells in the panel are shingled or not. The simulations also indicate that passivating the cut-face with a thermal oxide does not increase cell efficiency substantially. Therefore, doping schemes for the perimeter domain are suggested in order to increase efficiency levels above present standards. Finally, perimeter effects in cells that remain embedded in the wafer during the efficiency measurement are outlined.     

Spatially resolved analysis and minimization of resistive losses in high-efficiency Si solar cells

This paper presents an improved method for measuring the total lumped series resistance (R_s) of high-efficiency solar cells. Since this method greatly minimizes the influence of non-linear recombination processes on the measured R_s values, it is possible to determine R_s as a function of external current density over a wide range of illumination levels with a significantly improved level of accuracy. This paper furthermore explains how resistive losses in the emitter, the base, the metal/silicon contacts and the front metal grid can be separately determined by combining measurements and multidimensional numerical simulations. A novel combination of device simulation and circuit simulation is introduced in order to simulate complete 2 × 2 cm² PERL (‘passivated emitter and rear locally-diffused’) silicon solar cells. These computer simulations provide improved insight into the dynamics of resistive losses, and thus allow new strategies for the optimization of resistive losses to be developed. The predictions have been experimentally verified with PERL cells, whose resistive losses were reduced to approximately half of their previous values, contributing to a new efficiency world record (24.0%) for silicon solar cells under terrestrial illumination. The measurement techniques and optimization strategies presented here can be applied to most other types of solar cells, and to materials other than silicon.     

Individual differences in strategy use on division problems: Mental versus written computation.

Individual differences in strategy use (choice and accuracy) were analyzed. A sample of 362 Grade 6 students solved complex division problems under 2 different conditions. In the choice condition students were allowed to use either a mental or a written strategy. In the subsequent no-choice condition, they were required to use a written strategy. Latent class analysis showed that there were 3 subgroups of students with respect to pattern of strategy choices: primarily using a written strategy (more girls than boys); primarily using a mental strategy (more boys than girls); and using a written strategy on more difficult items but a mental strategy on the easier ones (almost no weak mathematical achievers). Strategy accuracies were analyzed with explanatory item response theory modeling. A between-subjects comparison in the choice condition showed that written strategies were usually more accurate than mental strategies, especially for the weak achievers. A within-subject comparison showed that the performance of students who used mental calculation on a particular item in the choice condition improved if they were required to use a written strategy in the no-choice condition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Social Thoughts and Beliefs Scale: A New Inventory for Assessing Cognitions in Social Phobia.

Development and initial psychometric features of a new inventory to assess cognitions associated with social phobia are described. The Social Thoughts and Beliefs Scale (STABS) is designed to assess cognitions in individuals with social phobia. In the 1st study, an initial pool of 45 items was reduced to 21. In the 2nd study, psychometric features of the scale were examined in a sample of individuals with social phobia, other anxiety disorders, and no psychiatric disorder. Total scores and two factor scores significantly differentiated individuals with social phobia from those in the other groups and were found to have adequate test-retest reliability and internal consistency. Potential usefulness of the STABS for assessing cognitions associated with social phobia is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A comparison of suicide and non-suicide deaths involving psychotropic drugs in four major U.S. cities

By use of a standard reporting form, extensive data were gathered on 651 deaths involving psychotropic drugs and recorded with the Coroner's or Medical Examiner's Office in each of four major U.S. cities. Thirty-six per cent of these deaths were listed as "Definitely Suicide" and 44% were listed as "Non-Suicide." A comparison was made of the age, sex, race, occupational category, and type of drug involved for each of these two groups, by city. In general, the Suicide group tended to be older, from higher occupational levels, and more often female. Blacks were under-represented among the Suicides but over-represented among the Non-Suicides. Suicide deaths tended to be associated with barbiturates, analgesics, and/or sedatives, while the Non-Suicides usually died from an accidental abuse of narcotics, usually heroin. These findings tended to be similar for each city, although some inter-city differences were noted.     

Long-Term Verification of Cover Systems Using Perfluorocarbon Tracers

The expanded use of caps and cover systems is an important aspect of the U.S. Department of Energy Environmental Management’s strategy for restoration and long-term stewardship of sites throughout the complex. However, very little is available in terms of long-term monitoring of covers other than downstream groundwater or surface water monitoring. A novel methodology for verifying and monitoring subsurface barriers and cover systems has been developed. Gaseous perfluorocarbon tracers (PFTs) are injected on one side of the barrier and searched for on the opposite side of the barrier. The capability for leak detection in subsurface barriers using PFTs has been proven at multiple demonstrations. Adaptation of this concept to covers is a necessary step prior to full-scale demonstration. This paper discusses the PFT technology and a successful proof-of-principle test of the PFT technology as a leak detection tool for cover verification and monitoring.     

Diagnostics for regression dependence in tables re-ordered by the dominant correspondence analysis solution

Correspondence analysis is an exploratory technique for analyzing the interaction in a contingency table. Tables with meaningful orders of the rows and columns may be analyzed using a model-based correspondence analysis that incorporates order constraints. However, if there exists a permutation of the rows and columns of the contingency table so that the rows are regression dependent on the columns and, vice versa, the columns are regression dependent on the rows, then both implied orders are reflected in the first dimension of the unconstrained correspondence analysis [Schriever, B.F., 1983. Scaling of order dependent categorical variables with correspondence analysis. International Statistical Review 51, 225-238]. Thus, using unconstrained correspondence analysis, we may still find that the data fit an ordinal stochastic model. Fit measures are formulated that may be used to verify whether the re-ordered contingency table is regression dependent in either the rows or columns. Using several data examples, it is shown that the fit indices may complement the usual geometric interpretation of the unconstrained correspondence analysis solution in low-dimensional space.     

Influence of flexible substrates on inverted organic solar cells using sputtered ZnO as cathode interfacial layer

Zinc oxide (ZnO) has recently shown to be of considerable interest for the development of interfacial buffer layers in inverted organic solar cells (OSCs). High quality ZnO thin films can indeed be prepared on large-area ITO-coated flexible substrates, using low temperature deposition techniques such as sputtering, a compatible technique with roll-to-roll process. However, further studies are still needed for a better understanding of the influence of the flexible substrate properties on the photovoltaic performances of those devices. In this work, ZnO films have been sputtered on ITO-coated flexible (PEN) substrates and annealed at different temperatures. The role of the surface morphology and the crystalline quality of ZnO films has been investigated. In the window of flexible compatible process, we found that moderate annealing temperatures of ZnO (?180 °C) lead to improved structural properties and performances. Interestingly, we achieve optimal performances for an annealing temperature of 160 °C, resulting in power conversion efficiency (PCE) equivalent to the highest performances usually achieved on rigid cells.     

Efficient in situ electroporation of mammalian cells grown on microporous membranes

Electroporation is a common technique for the introduction of DNA molecules into living cells. The method is currently limited by the necessity of applying the electrical discharge to cells in suspension. Adherent cells must therefore be removed from their substratum, which can induce unwanted physiological effects. We report here a new procedure for in situ electroporation of cells grown on microporous membranes of polyethylene terephthalate (PET) or polyester (PE). We demonstrate that this method of in situ electroporation employs only readily available materials and standard electroporation devices without any modifications, is as efficient as conventional electroporation of cells in suspension, and is applicable to a wide range of cell types. Efficient electroporation can be achieved under conditions of minimal cell killing, and can be performed with quiescent cells as well as with confluent epithelial sheets. The method is a useful extension of electroporation technology, and will allow the application of electroporation to a wider spectrum of biological systems.