The risk of being shot at: Stress, cortisol secretion, and their impact on memory and perceived learning during reality-based practice for armed officers.

A field experiment was organized during a handgun shooting workshop for armed officers (N = 36). In-depth stress analyses involved anticipatory distress, subjective stress, and salivary cortisol reactivity triggered by reality-based handgun shooting practice and, more specifically, by being in an uncontrollable situation with the risk of being shot at. Subsequently, the study examined to what extent exposure to reality-based stress affected working memory performances and self-perceived active learning. As expected, the risk of being shot at caused more anticipatory distress, subjective stress, and increasingly triggered cortisol secretion. Further results showed that, although stress endurance deteriorated working memory performance, participants in the high-realism group simultaneously self-perceivably learned more (i.e., acquired task-relevant skills and competencies). The dual stress effect may result from the professional appreciation of reality-based practice and increased self-efficacy toward hazardous real-life situations. Balancing the intersection between occupational psychology, cognitive psychology, and psychoneuroendocrinology, this study performed stress research in an important and rarely accessible professional setting. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Process modeling for doped regions formation on high efficiency crystalline silicon solar cells

Process modeling approaches derived from CMOS industry are successfully applied in the Photovoltaic industry, in order to provide guidance on the design of the doped regions. The accurate prediction of the dopant diffusion and activation kinetics, as well the oxide growth rate, are essential for the adequate profile engineering. The latter is vital for a cost effective optimization of the cell operation. In addition, in the case of ion implantation, TCAD modeling is also necessary for the monitoring of the damage evolution and its optimized reduction. Indeed, high levels of residual defects are found to deteriorate the electrical properties of the doped regions, as they act as recombination centers for Shockley-Read-Hall recombination and thus limit the minority carrier lifetimes. Designing optimum anneal strategies is an important objective of the TCAD modeling approach. In this paper we are presenting an overview of our developments to optimize TCAD simulations for doped regions formation used in high efficiency crystalline silicon solar cells. The modeling studies cover the two major dopant techniques (tube diffusion and ion implantation) for each dopant (Boron and Phosphorus).     

Demanufacturing photovoltaic panels: Comparison of end-of-life treatment strategies for improved resource recovery

Predictive models to forecast the volume and material composition of end-of-life photovoltaic (PV) panels indicate that substantial material resources can potentially be recovered from silicon based PV panels in the next decades. The technical feasibility of selective mechanical delamination through milling and cleaving was experimentally studied. The achievable material recovery results are compared to current practices in end-of-life treatment, demonstrating a substantial potential to improve resource preservation. A comparative LCA study allows to conclude that a well-designed demanufacturing strategy based on selective delamination can substantially reduce the environmental impact associated with end-of-life processing of PV panels. The improved silver recovery offers perspectives for the economic viability of the described demanufacturing strategy.     

Boron‐doped selective silicon epitaxy: high efficiency and process simplification in interdigitated back contact cells

The present research and development activities in crystalline silicon photovoltaics include the exploration of doping technologies alternative to the mainstream diffusion process. The goal is to identify those technologies with potential to increase the solar cell efficiency and reduce the cost per watt peak. In that respect, this work presents the selective epitaxial growth of silicon as a candidate for boron doping; showing the results of the evaluation of boron‐doped silicon epitaxial emitters on slurry and diamond‐coated wire‐sliced Czochralski material, their integration in interdigitated back contact solar cells, and the development of a novel process sequence to create the interdigitated rear junction of these devices using selective epitaxial growth. Boron‐doped silicon epitaxy is demonstrated to perform in the high efficiency range (>22%), and the use of selective epitaxial growth is proposed as a route for the simplification of the interdigitated back contact solar cell flow. Copyright © 2013 John Wiley & Sons, Ltd.     

Evaluation of the influence of an embedded porous silicon layer on the bulk lifetime of epitaxial layers and the interface recombination at the epitaxial layer/porous silicon interface

Porous silicon plays an important role in the concept of wafer‐equivalent epitaxial thin‐film solar cells. Although porous silicon is beneficial in terms of long‐wavelength optical confinement and gettering of metals, it could adversely affect the quality of the epitaxial silicon layer grown on top of it by introducing additional crystal defects such as stacking faults and dislocations. Furthermore, the epitaxial layer/porous silicon interface is highly recombinative because it has a large internal surface area that is not accessible for passivation. In this work, photoluminescence is used to extract the bulk lifetime of boron‐doped (10¹⁶/cm³) epitaxial layers grown on reorganised porous silicon as well as on pristine mono‐crystalline, Czochralski, p⁺ silicon. Surprisingly, the bulk lifetime of epitaxial layers on top of reorganised porous silicon is found to be higher (~100–115 µs) than that of layers on top of bare p⁺ substrate (32–50 µs). It is believed that proper surface closure prior to epitaxial growth and metal gettering effects of porous silicon play a role in ensuring a higher lifetime. Furthermore, the epitaxial layer/porous silicon interface was found to be ~250 times more recombinative than an epitaxial layer/p⁺ substrate interface (S ≅ 10³ cm/s). However, the inclusion of an epitaxially grown back surface field on top of the porous silicon effectively shields minority carriers from this highly recombinative interface. Copyright © 2013 John Wiley & Sons, Ltd.     

Modeling of Nucleation and Growth of M23C6 Carbide in Multi-component Fe-based Alloy

Three-dimensional atom probe (3DAP) technique has been used to study the nucleation and growth of M23C6 carbide in a supersaturated multi-component Fe-based alloy aged at 800°C. 3D images indicate that the radius of M23C6 carbide after ageing for 10 min is about 9 nm. Concentration profiles of alloy elements in the carbide are also obtained. Combined with PANDAT and Thermo-Calc software, attempts to model the early stages of precipitation are present. The calculated particle size and composition of M23C6 carbide is in good agreement with 3DAP data.     

Magnetic field oriented tetragonal zirconia with anisotropic toughness

(0 0 1)-oriented 3 mol% yttria stabilized tetragonal zirconia (3Y-TZP) has been developed by reactive synthesis of undoped pure monoclinic zirconia and co-precipitated 8 mol% yttria-stabilized zirconia (8Y-ZrO₂). The dispersed pure monoclinic ZrO₂ powder, having magnetic anisotropy, was first aligned in a strong magnetic field and co-sintered in a randomly distributed cubic 8Y-ZrO₂ fine matrix powder. The reactive sintering resulted in a 3Y-TZP ceramic with a (0 0 1) orientation. The (0 0 1)-oriented 3Y-TZP showed a substantial toughness anisotropy, i.e. the toughness along the [0 0 1] direction is 54% higher than that of its perpendicular direction. Moreover, the toughness along the [0 0 1] direction is 49% higher than that of a non-textured isotropic reactively synthesized 3Y-TZP and 110% higher than that of an isotropic co-precipitated powder based 3Y-TZP. The substantially enhanced toughness was interpreted in terms of the tetragonal to monoclinic martensitic phase transformability.     

Passivation of photonic nanostructures for crystalline silicon solar cells

We report on the optical and electrical performances of periodic photonic nanostructures, prepared by nanoimprint lithography (NIL) and two different etching routes, plasma, and wet chemical etching. Optically, these periodic nanostructures offer a lower integrated reflectance compared with the industrial state‐of‐the‐art random pyramid texturing. However, electrically, they are known to be more challenging for solar cell integration. We propose the use of wet chemical etching for fabricating inverted nanopyramids as a way to minimize the surface recombination velocities and maintain a conventional cell integration flow. In contrast to the broadly used plasma etching for nanopatterning, the wet chemically etched nanopatterning results in low surface recombination velocities, comparable with the state‐of‐the‐art random pyramid texturing. Applied to 40‐µm thick epitaxially grown crystalline silicon foils bonded to a glass carrier superstrate, the periodic‐inverted nanopyramids show carrier lifetimes comparable with the non‐textured reference foils (τ_eff = 250 µs). We estimate a maximum effective surface recombination velocity of ~8 cm/s at the patterned surface, which is comparable with the state‐of‐the‐art values for crystalline silicon solar cells. Copyright © 2014 John Wiley & Sons, Ltd.     

Three-dimensional phase-field simulation of microstructural evolution in three-phase materials with different diffusivities

The coarsening behavior of three-phase materials, such as eutectic material systems, is of high technological interest. Microstructure evolution simulations can help to understand the effect of different magnitudes of the diffusivities in the different phases. In this study, the evolution of a 3D three-phase morphology was modeled with equal interfacial energy and volume fraction and similar thermodynamic properties for the three phases, but the diffusion mobilities were taken different. It was observed that the phase with the lowest mobility has the highest growth rate and, on average, a larger number of grain faces, while the other two phases have a nearly equal growth rate and average number of grain faces. The simulation results are compared with results from experiments and simulation studies for single-phase and two-phase materials.