bluuebunny/crossref_metadata_2025_split huggingface dataset:
Processing and Characterization of Efficient Thin-Film Polycrystalline-Silicon Solar Cells
Authors: Gordon Ivan , Van Gestel Dries , Qiu Yu , Venkatachalam Srisaran , Beaucarne Guy , Poortmans Jef 
Published: April 2011

AbstractEfficient thin-film polycrystalline-silicon (pc-Si) solar cells on inexpensive substrates could substantially lower the price of photovoltaic electricity. We recently showed that good solar cells can be made from pc-Si obtained by epitaxial thickening using thermal CVD of a seed layer made by aluminium-induced crystallization (AIC) of amorphous silicon. We already reported cells in substrate configuration with energy conversion efficiencies up to 8.0% for layers on ceramic alumina substrates. However, much higher efficiencies (η > 10%) are needed for this type of pc-Si solar cells to become cost-effective. To achieve these higher efficiencies, cells will probably have to be made in a superstrate configuration on transparent substrates and advanced light trapping will need to be applied. In this paper we report on our recent progress with pc-Si solar cells made on transparent glass-ceramic substrates.So far, our best pc-Si solar cells in substrate configuration on glass-ceramics showed an efficiency of 6.4%. By using plasma texturing to lower the front side reflection, we increased the current density of our cells by roughly 1 mA cm-2. The Jsc is much lower for cells on glass-ceramic than for cells on alumina. This is the result of the better diffuse back reflectance of alumina compared to glass. The Voc and fill factor are comparable for cells on both substrates.To make pc-Si solar cells on glass in superstrate configuration, we will use a-Si/c-Si rear junction emitters. As a first test of the feasibility of this approach, we measured the illuminated IV parameters of pc-Si cells made for the substrate configuration in superstrate configuration. In superstrate configuration, the current density of the cells is much lower than in substrate configuration due to the non-optimized cell design for superstrate illumination. The Voc is slightly smaller in superstrate configuration due to the lower current density.These results indicate that the glass-ceramic substrates are fully compatible to our poly-Si solar cell process. Furthermore, rear-junction poly-Si cells in superstrate configuration should lead to good cell results once the absorber layer thickness is optimized to the diffusion length of the material and light trapping features adapted to the superstrate configuration are applied.
Up-and Down-Conversion,and Multi-Exciton Generation for Improving Solar Cells:A Reality Check
Authors: Shpaisman Hagay , Niitsoo Olivia , Lubomirsky Igor , Cahen David 
Published: April 2011

AbstractBecause conventional photovoltaic (PV) cells are threshold systems in terms of optical absorption, “photon management“is an obvious way to improve their performance.Calculations to optimize photon utilization in a single-junction PV cell show ˜1.4 eV to be the optimal bandgap for terrestrial solar to electrical power conversion. For Si, with a slightly sub-optimal gap, continuous efforts have yielded single-junction laboratory cells, quite close to the theoretical limit.One of the repeatedly proposed directions to improve photon management is that of up- and down-conversion of photon energy. In up-conversion two photons with energy hv < EG (the band gap) create one photon with hv > EG, while in down-conversion one photon with energy hv > 2EG, yields two photons with energy hv > EG.Multi-exciton generation (MEG), although not a "photon management" process, can achieve effects like down-conversion, which, though, is more limited than MEG. In MEG one photon with energy hv > nEG yields n electron-hole pairs with energy EG. Because MEG has clear advantages over down-conversion, in the following we will, instead of considering both, consider MEG.We find that a straightforward analysis of this approach to “photon management” for a single junction cell under the detailed balance limit shows clearly that, even if we assume (highly unrealistic) 100% efficient up-conversion and MEG, a new theoretical PV conversion limit of 49 %, instead of 31% is arrived at, a maximum possible gain of ≈60%. The main attractive feature of the combination of up-conversion and MEG is a significant broadening of the optimal band-gap range. Rough estimates for the very highest possibly feasible efficiencies for up-conversion and MEG (25% and 70% respectively), yield at most slightly less than 40% PV conversion efficiency, i.e., only a ˜25% gain over conventional single band gap semiconductor.These results show that up-conversion or MEG are fascinating scientific areas of research, whose implementation can indeed improve PV cell performance. However, truly formidable challenges need to be met to have UC + MEG lead to the type of radical decrease in the (cost)/ (efficiency × lifetime × yield) ratio that we need to allow large-scale economic introduction of PV cells. Parallel pursuit of alternative approaches to improved photon management, such as, for example, lowering the costs of arrangements with multiple solar absorbers and/or multi-junction systems, appears, therefore, critical for the future of PV.
Enhanced Light-trapping in Solar Cells by Directional Selective Optical Filters
Authors: Ulbrich Carolin , Kirchartz Thomas , Rau Uwe 
Published: April 2011

AbstractDirectional selective optical filters increase the photon confinement of solar cells with a Lambertian light-trapping scheme. These filters restrict the transmission of incoming sunlight to a cone of limited acceptance angle. This paper models the efficiency gain or loss caused by an ideal directional and energy selective filter on top of a solar cell, and compares it to a cell with Lambertian surface and a planar absorber. The enhancement of light trapping by the directional filter is illustrated by the enhancement of the quantum efficiency of normally incident light. Simulations of the annual yield demonstrate that the improved light trapping results in an overall energy gain of more than 10 % for a tracked system.To achieve this gain at the equator,a filter with small acceptance angle of 5 ° that is active below the threshold energy ˜1.5 eV has to used.
Size-Controlled Silicon Quantum Dots Superlattice for Thin-Film Solar Cell Applications
Authors: Kurokawa Yasuyoshi , Miyajima Shinsuke , Yamada Akira , Konagai Makoto 
Published: April 2011

AbstractWe prepared size-controlled silicon quantum dots superlattices (Si-QDSLs) by thermal annealing of stoichiometric hydrogenated amorphous silicon carbide (a-SiC:H)/silicon rich hydrogenated amorphous silicon carbide (a-Si1+xC:H) multilayers for thin-film solar cell applications. Transmission electron microscope (TEM) observation revealed that the size of silicon quantum dots can be controlled by the thickness of the a-Si1+xC:H layers. It was found that hydrogen plasma treatment (HPT) significantly enhanced the photoluminescence (PL) of the Si-QDSLs. From the results of the PL measurement, the bandgap of the Si-QDSLs can be controlled from 1.1 eV to 1.6 eV by varying the diameter of silicon quantum dots. ESR measurement indicated that HPT reduced the defect density in a Si-QDSL from 1.83 ×1019 to 1.67 sup1018 cm-3.
Optical Enhancement by Textured Back Reflector in Amorphous and Nanocrystalline Silicon Based Solar Cells
Authors: Yan Baojie , Yue Guozhen , Jiang Chun-Sheng , Yan Yanfa , Owens Jessica M. , Yang Jeffrey , Guha Subhendu 
Published: April 2011

AbstractWe present the results of systematic studies of optical enhancements by textured Ag/ZnO back reflectors in a-SiGe:H and nc-Si:H solar cells. First, the back reflector materials were characterized by AFM, XRD, and TEM. The results showed that the ZnO layers deposited by sputtering exhibit an increased surface texture with the deposition temperature and film thickness. The material structure showed a strong (002) preferential orientation. The large columnar crystal structure determines the surface texture. Second, the solar cell performance was correlated to the back reflector structure. We found that with a thin ZnO layer, a textured Ag layer results in more light scattering than a flat Ag layer. However, when a thick ZnO layer is used, a flat Ag layer can produce similar or more light scattering than a textured Ag layer. Third, we developed a method to estimate the optical enhancement for a-SiGe:H and nc-Si:H solar cells on various structures of Ag/ZnO back reflectors. Comparing the quantum efficiency data from solar cells made using the same recipe but one on a flat stainless steel substrate and another on a textured Ag/ZnO BR substrate revealed that the optical enhancement for the long wavelength light can be as high as 20 to 30. Compared to the theoretical value of 4n2, there is still scope for further improvement
Quantum Dot Solar Cells Based on CdSe-Assembled Titania Semiconductors
Authors: Wang Chien-Tsung , Yeh Chung-Hsiao 
Published: April 2011

AbstractIn the study, semiconductor quantum dots (QDs) of CdSe nanocrystals have been demonstrated effective as the light energy harvesting assemblies in solar cells. Colloidal CdSe QDs were synthesized by the one-pot approach and linked through a surface modifier onto titania (TiO2) nanoparticles. The TiO2-CdSe composite, while employed as the photoanode in a photoelectrochemical apparatus, exhibited a higher photon-to-electron conversion efficiency (3-fold) than the TiO2 alone, and also a higher stability for photocurrent generation, according to photocurrent transient responses. The optical absorbance and photoluminescence of the CdSe colloid showed a blue shift in the absorption edge with decreasing the particle size (band energy gap shifts from 2.0 to 2.19 eV), suggesting a quantum size effect. The CdSe particle size was determined up to 5 nm by a transmission electron microscopy. A scheme describing the charge carrier rectification for the coupled semiconductor system is proposed.
Organic:PbS-nanocrystal:Fullerene Hybrid Photovoltaics
Authors: Dissanayake Nanditha , Hatton Ross A , Giusca Cristina , Lutz Thierry , Curry Richard , Silva Ravi 
Published: April 2011

AbstractSingle and multi junction hybrid devices comprising oligoacenes, PbS quantum dots (PbS-QD) and C60 are demonstrated. A greatly improved performance of the PbS-QD /C60 system was obtained in this work. Furthermore, a study of using acenes (pentacene, tetracene) as light absorbers and photoinduced electron donors to PbS-QD was carried out. Fabricated devices were characterized under 1 Sun simulated solar irradiation and external quantum efficiency (EQE) measurements. The initial hybrid devices demonstrated up to 0.14 % power conversion efficiency under AM1.5G illumination and up to 16 % EQE at 400 nm. The single junction (PbS-QD/C60) devices demonstrated greater than 1.2 % EQE at 1100 nm while multi junctional tetracene/PbS-QD/C60 devices exhibited up to 0.2 % EQE in the infrared region (1100 nm). Ultraviolet photoelectron spectroscopy was used to measure the molecular energy levels in the system under discussion to justify the photoinduced charge transfer. This work demonstrates new device systems which can be potentially be utilized to fabricate high efficient broad band absorbing hybrid photovoltaics.
High Pressure Phase Transformations in Heavy Rare Earth Metals and Connections to Actinide Crystal Structures
Authors: Vohra Yogesh K. , Sangala Bagvanth Reddy , Stemshorn Andrew K. , Hope Kevin M. 
Published: April 2011

AbstractHigh-pressure studies have been performed on heavy rare earth metals Terbium (Tb) to 155 GPa and Holmium (Ho) to 134 GPa in a diamond anvil cell at room temperature. The following crystal structure sequence was observed in both metals hcp ⟶ Sm-type ⟶ dhcp ⟶ distorted fcc (hR-24) ⟶ monoclinic (C2/m) with increasing pressure. The last transformation to a low symmetry monoclinic phase is accompanied by a volume collapse of 5 % for Tb at 51 GPa and a volume collapse of 3 % for Ho at 103 GPa. This volume collapse under high pressure is reminiscent of f-shell delocalization in light rare earth metal Cerium (Ce), Praseodymium (Pr), and heavy actinide metals Americium (Am) and Curium (Cm). The orthorhombic Pnma phase that has been reported in Am and Cm after f-shell delocalization is not observed in heavy rare earth metals under high pressures.
Theory of Photoemission in Actinides
Authors: Svane Axel 
Published: April 2011

AbstractA theory is presented which describes the photoemission spectra of actinide compounds starting from the atomic limit of isolated actinide ions. The multiplets of the ion are calculated and an additional term is introduced to describe the interaction with the sea of conduction electrons. This leads to complex mixed-valent ground states, which describes well the rich spectrum observed for PuSe. In particular, the three-peak feature, which is often seen in Pu and Pu compounds in the vicinity of the Fermi level originates from f6 → f5 emission. The theory is further applied to PuSb, PuCoGa5 and Am.
Accelerated Dissolution Process of the Spent Fuel (UO2) under Repository Conditions
Authors: Iglesias Eduardo , Quiñones Javier , Rodriguez Nieves 
Published: April 2011

AbstractNowadays, nuclear energy is one of the options for developed countries in order to maintain the demand of electric energy. One of the problems of this kind of energy generation is the residual waste form after a fuel cycle (spent fuel). These kind of material is so difficult to characterize -due to their composition and the thermal treatment in the reactor- that exhaustive studies are necessaries for a complete knowledge, helping to build, with complete reliability, a very safety underground facility. In this way, the option known as Deep Geological Repository (DGR) is been developed by each country taking part in the nuclear energy industry. The unique via for the migration to the biosphere of the radionuclides -actinides and lanthanides content in the spent fuel pellet (UO2) after the closing of the deep geological repository is by the water transport phenomena. It is a fundamental question to know how much time they will spend in their trip; and the first step is the rate of liberation of these radionuclides from the spent fuel pellet. In this way, the matrix dissolution rate of the spent fuel pellet no dependent on the specific surface area after a normalization by the initial value- is a key parameter to begin the performance assessment for any deep geological repository and the specific surface value is, following the Matrix Alteration Model (MAM) sensitivity analysis, one of the most important parameters controlling the radionuclides liberation. In this way, several measurements were carried out to obtain values in different conditions for different sieves of UO2 powder, treated as fresh fuel. First of all, the specific surface area was measured with a multi-point isothermal procedure with N2 and Kr, the both. The values obtained were presented in order to obtain a general law for the evolution with the particle size. These data are part of a bigger project about the complete description of the spent fuel analogous; very useful to obtain new dissolution rates for the spent fuel under repository simulated conditions.
Toward Modeling Charge-Defect Reactions at the Atomistic Level
Authors: Valone Steve 
Published: April 2011

AbstractDefect reactions involving charged species are commonplace in nuclear fuels fabrication and burn-up. Even the simplest of these fuels, uranium dioxide (UO2), typically involves the nominal charge states of +3, +4, and +5 or +6 in U and -1 and -2 states in O. Simulations that attempt to model evolutionary processes in the fuels require tracking changes among these charge states. At the atomistic level, modeling defect reactions poses a particularly vexing problem. Typical potential energy surfaces do not have this type of physical phenomena built into them. Those models that do attempt to model charge-defect reactions do not have especially strong physical bases for the models. For instance, most do not obey established limits of charge behavior at dissociation or lack internal consistency. This work presents substantial generalizations to earlier work of Perdew et al. No matter the size of the system, total system hamiltonians can be decomposed into subsystem or site hamiltonians and coulombic interactions. Site hamiltonians can be evaluated in a spectral representation, once an integer number of electrons are assigned. For both pair and individual site hamiltonians a dilemma emerges in that many sites are better understood as possessing a fractional charge. The dilemma is how to weight the site integer-charge states in a physically consistent manner. One approach to solving the dilemma results in two distinct charge-dependent energy contributions emerge, arising from intra- and inter-subsystem charge transfer. Further analysis results in a model of the intra-subsystem charge-transfer that can accommodate the mixed valence states of either U or O in nuclear fuels. Mixed valence properties add complications to the model that originate in the phenomenological fact that it typically requires different amounts of energy to increase or decrease charge. As a result of the inherent complexity one has the option of using multiple charges, a concept with strong ties to shell models, or modeling parameters not directly related to charge as functions of charge. This latter approach is illustrated by invoking a minimization principle that does preserve the important dissociation limits of Perdew et al., in order to complete the model.
Intrinsically Localized Modes in Uranium and the Prospect for Finding them in Plutonium
Authors: Manley Michael 
Published: April 2011

AbstractDynamic nonlinear localization, an emerging new area of materials physics, has the potential to fundamentally change our understanding of materials properties. These intrinsically localized modes (ILM) have been found forming in uranium above about 450 K. Comparisons with data from the literature shows that these ILMs influence many properties, including heat capacity, thermal transport, thermal expansion, and mechanical deformation. The existence of ILMs helps to explain many anomalies in uranium, some of which have been known for more than fifty years. Here, the possibility that ILMs may also play a role in the properties of plutonium is considered. The mechanism helps to explain the success of an “Invar-like” two-level model for the thermal expansion of Pu without the need to invoke local magnetic states, which have been ruled out experimentally. It also helps to explain an excitation observed in δ-plutonium that has energy consistent with the two-level model, but momentum dependence consistent with lattice vibrations. This excitation, energy and momentum dependence, is consistent with the non-equilibrium generation of ILMs and the thermal excitation properties of these ILMs are consistent with a two-level model. High-temperature inelastic x-rays scattering measurements of the phonon dispersion curves of δ-plutonium are needed to test this hypothesis.
Find the Nano in Your Life: Using Interactive Museum Demonstrations to Engage a Public Audience in Nanotechnology Research and Policy
Authors: Das Jayatri , Francies Allison B. , Redwing Ronald D. 
Published: April 2011

AbstractTo many Americans, nanotechnology remains a science of the future; most are unaware that nanoscale science is already being incorporated into products they use in their everyday lives. Informal learning environments are an ideal venue in which to not only educate the public about current applications of nanotechnology but also engage them in a discussion of its impacts. Developed through a partnership between two NSF-funded Materials Research Science and Engineering Centers at Penn State and Cornell Universities and The Franklin Institute in Philadelphia, the “Small Wonders: Find the Nano in Your Life” program has been distributed to 20 science and children's museums around the United States. This cart-based program includes interactive demonstrations of commercially available products that use nanoscale technology, including sunblock, nanosilver food containers, and nanoiron for environmental remediation. Macroscale models enable visitors to understand the underlying science, while real products allow visitors to explore the hope, hype, and reality of each. Here, we discuss the educational goals of the program, our approach to presenting questions of both science and policy, and methods and results of visitor evaluation. This third collaborative project continues to build on a model of program development and distribution that has been highly successful at reaching a broad audience.
The Humacao Strange Matter Exhibition: Prem Brings Materials Science and Nanotechnology to Puerto Rican Communities
Authors: Ramos Idalia , Rivera Ramón A. , Pinto Nicholas J. , Sotero José , Vega Esther , Zimbovskaya Natalya , Negrón Pablo , Rivera Mirza , Colón Gladys 
Published: April 2011

AbstractThe “UPRH-PENN Partnership for Research and Education in Materials” (PREM) is sponsored by the Division of Materials Research of the National Science Foundation and since 2004 it has contributed to increasing the participation of Puerto Rican men and women in materials research and education. The program integrates K-12, undergraduates, graduate students, and faculty collaborating through research and education in a partnership between the University of Puerto Rico at Humacao (UPRH) along with UPRC and UPRRP and the University of Pennsylvania Materials Research Science & Engineering Center. The UPRH-PREM has strong links with schools in the eastern region of Puerto Rico and has successfully integrated K-12 students and teachers into the program through workshops, web resources, open houses, a Summer Program and research experiences during the academic year. In an effort to integrate the wider community into the outreach efforts, from October to December 2007 PREM hosted the presentation of the Interactive Materials Science Exhibition “Strange Matter”. “Strange Matter” was designed and produced by the Materials Research Society (MRS) in conjunction with the Ontario Science Centre in Toronto. Funding for the project is being provided by the National Science Foundation and industrial partners 3M, Dow, Ford, Intel, and Alcan. The exhibition brings interactive activities that highlight the fact that materials science is all around us. This exhibition is the first and only one in the island of Puerto Rico and was presented at UPRH's Casa Roig Museum, a historic plantation house located in downtown Humacao. Local scientists complemented the exhibition with live demonstrations and talks to provide deeper explanations and motivate young visitors to study materials. To make the exhibition possible, PREM integrated UPR-Humacao administration, faculty, students, non-teaching workers, Casa Roig staff, schools, Humacao municipality, local businesses and individual citizens. Dozens of students, faculty and other members of the community were mobilized as volunteers to support all aspects of the exhibition.