Open Access. Powered by Scholars. Published by Universities.®
Physical Sciences and Mathematics Commons™
Open Access. Powered by Scholars. Published by Universities.®
- Institution
- Publication Year
- Publication
- Publication Type
Articles 1 - 15 of 15
Full-Text Articles in Physical Sciences and Mathematics
Data-Driven Approaches To Complex Materials: Applications To Amorphous Solids, Dil Kumar Limbu
Data-Driven Approaches To Complex Materials: Applications To Amorphous Solids, Dil Kumar Limbu
Dissertations
While conventional approaches to materials modeling made significant contributions and advanced our understanding of materials properties in the past decades, these approaches often cannot be applied to disordered materials (e.g., glasses) for which accurate total-energy functionals or forces are either not available or it is infeasible to employ due to computational complexities associated with modeling disordered solids in the absence of translational symmetry. In this dissertation, a number of information-driven probabilistic methods were developed for the structural determination of a range of materials including disordered solids to transition metal clusters. The ground-state structures of transition-metal clusters of iron, nickel, and …
Large And Realistic Models Of Amorphous Silicon, Dale Ingram, Bishal Bhattarai, Parthapratim Biswas, David A. Drabold
Large And Realistic Models Of Amorphous Silicon, Dale Ingram, Bishal Bhattarai, Parthapratim Biswas, David A. Drabold
Faculty Publications
Amorphous silicon (a-Si) models are analyzed for structural, electronic and vibrational characteristics. Several models of various sizes have been computationally fabricated for this analysis. It is shown that a recently developed structural modeling algorithm known as force-enhanced atomic refinement (FEAR) provides results in agreement with experimental neutron and X-ray diffraction data while producing a total energy below conventional schemes. We also show that a large model (∼ 500 atoms) and a complete basis is necessary to properly describe vibrational and thermal properties. We compute the density for a-Si, and compare with experimental results.
Amorphous And Micromorph Si Solar Cells: Current Status And Outlook, Vitaliy Avrutin, Natalia Izyumskaya, Hadis Morkoç
Amorphous And Micromorph Si Solar Cells: Current Status And Outlook, Vitaliy Avrutin, Natalia Izyumskaya, Hadis Morkoç
Turkish Journal of Physics
An overview of the current status and prospects of thin-film Si photovoltaics, including both hydrogenated amorphous and microcrystalline Si as well their combination known as micromorph solar cells, with a major focus on the technological development is given. Although thin-film Si solar cells have been one of the first commercially successful photovoltaic devices, today they face a tremendous challenge from variety of bulk Si technologies (mono- and multicrystalline Si) and compound-semiconductor thin-film solar cells, both of which have managed to substantially reduce the production cost and improve power conversion efficiency. Thin-film Si photovoltaics benefiting from the mighty mainstream Si industry …
Carrier Drift-Mobilities And Solar Cell Models For Amorphous And Nanocrystalline Silicon, Eric A. Schiff
Carrier Drift-Mobilities And Solar Cell Models For Amorphous And Nanocrystalline Silicon, Eric A. Schiff
Physics - All Scholarship
Hole drift mobilities in hydrogenated amorphous silicon (a-Si:H) and nanocrystalline silicon (nc-Si:H) are in the range of 10-3 to 1 cm2/Vs at room-temperature. These low drift mobilities establish corresponding hole mobility limits to the power generation and useful thicknesses of the solar cells. The properties of as-deposited a-Si:H nip solar cells are quite close to their hole mobility limit, but the corresponding limit has not been examined for nc-Si:H solar cells. We explore the predictions for nc-Si:H solar cells based on parameters and values estimated from hole drift-mobility and related measurements. The indicate that the hole mobility limit for nc-Si:H …
An Investigation Of The Effects Of Hydrogen On Local Strain Fields And Structural Disorder-To-Order Transition In Hydrogenated Amorphous Silicon, Aniekan Magnus Ukpong
An Investigation Of The Effects Of Hydrogen On Local Strain Fields And Structural Disorder-To-Order Transition In Hydrogenated Amorphous Silicon, Aniekan Magnus Ukpong
Turkish Journal of Physics
This study utilizes the fluctuations in the mean silicon-silicon near neighbour distances and local atomic-level stresses to study the chemically-induced disorder-to-order transition in hydrogenated amorphous silicon as a function of hydrogen concentration C_H. The correlation between a suitable stress and structure parameter shows a three-stage structure transition that culminates in the formation of a crystalline phase at high C_H. In the low C_H limit, the structural changes are characterized by a linear response to stress giving a rigidity modulus of 73.43+-15 GPa. In the intermediate and high C_H limits, the stress-structure correlation shows a volume-dependence. At very high hydrogen concentrations, …
Hole Mobility Limit Of Amorphous Silicon Solar Cells, Jiang Liang, Eric A. Schiff, S. Guha, Baojie Yan, Jeff Yang
Hole Mobility Limit Of Amorphous Silicon Solar Cells, Jiang Liang, Eric A. Schiff, S. Guha, Baojie Yan, Jeff Yang
Physics - All Scholarship
We present temperature-dependent measurements and modeling for a thickness series of hydrogenated amorphous silicon nip solar cells. The comparison indicates that the maximum power density (PMAX) from the as-deposited cells has achieved the hole-mobility limit established by valence bandtail trapping, and PMAX is thus not significantly limited by intrinsic-layer dangling bonds or by the doped layers and interfaces. Measurements of the temperature-dependent properties of light-soaked cells show that the properties of as-deposited and light-soaked cells converge below 250 K; a model perturbing the valence band tail traps with a density of dangling bonds accounts adequately for the convergence effect.
Temperature-Dependent Open-Circuit Voltage Measurements And Light-Soaking In Hydrogenated Amorphous Silcon Solar Cells, Jianjun Liang, Eric A. Schiff, S. Guha, Baojie Yan, Jeff Yang
Temperature-Dependent Open-Circuit Voltage Measurements And Light-Soaking In Hydrogenated Amorphous Silcon Solar Cells, Jianjun Liang, Eric A. Schiff, S. Guha, Baojie Yan, Jeff Yang
Physics - All Scholarship
We present temperature-dependent measurements of the open-circuit voltage VOC(T) in hydrogenated amorphous silicon nip solar cells prepared at United Solar. At room-temperature and above, VOC measured using near-solar illumination intensity differs by as much as 0.04 V for the as-deposited and light-soaked states; the values of VOC for the two states converge below 250 K. Models for VOC based entirely on recombination through deep levels (dangling bonds) do not account for the convergence effect. The convergence is present in a model that assumes the recombination traffic in the as-deposited state involves only bandtails, but which splits the recombination traffic fairly …
Low-Mobility Solar Cells: A Device Physics Primer With Application To Amorphous Silicon, Eric A. Schiff
Low-Mobility Solar Cells: A Device Physics Primer With Application To Amorphous Silicon, Eric A. Schiff
Physics - All Scholarship
The properties of pin solar cells based on photogeneration of charge carriers into lowmobility materials were calculated for two models. Ideal p- and n-type electrode layers were assumed in both cases. The first, elementary case involves only band mobilities and direct electron–hole recombination. An analytical approximation indicates that the power in thick cells rises as the 1 4 power of the lower band mobility, which reflects the buildup of space-charge under illumination. The approximation agrees well with computer simulation. The second model includes exponential bandtail trapping, which is commonly invoked to account for very low hole drift mobilities in amorphous …
Bandtail Limits To Solar Conversion Efficiencies In Amorphous Silicon Solar Cells, Kai Zhu, Weining Wang, Eric A. Schiff, Jianjun Liang, S. Guha
Bandtail Limits To Solar Conversion Efficiencies In Amorphous Silicon Solar Cells, Kai Zhu, Weining Wang, Eric A. Schiff, Jianjun Liang, S. Guha
Physics - All Scholarship
We describe a model for a-Si:H based pin solar cells derived primarily from valence bandtail properties. We show how hole drift-mobility measurements and measurements of the temperature-dependence of the open-circuit voltage VOC can be used to estimate the parameters, and we present VOC(T) measurements. We compared the power density under solar illumination calculated with this model with published results for as-deposited a-Si:H solar cells. The agreement is within 4% for a range of thicknesses, suggesting that the power from as-deposited cells is close to the bandtail limit.
Hole Drift-Mobility Measurements In Contemporary Amorphous Silicon, S. Dinca, Eric A. Schiff, V. Vlahos, C. R. Wronski, Q. Yuan
Hole Drift-Mobility Measurements In Contemporary Amorphous Silicon, S. Dinca, Eric A. Schiff, V. Vlahos, C. R. Wronski, Q. Yuan
Physics - All Scholarship
We present hole drift-mobility measurements on hydrogenated amorphous silicon from several laboratories. These temperature-dependent measurements show significant variations of the hole mobility for the differing samples. Under standard conditions (displacement/field ratio of 2×10-9 cm2/V), hole mobilities reach values as large as 0.01 cm2/Vs at room-temperature; these values are improved about tenfold over drift-mobilities of materials made a decade or so ago. The improvement is due partly to narrowing of the exponential bandtail of the valence band, but there is presently little other insight into how deposition procedures affect the hole drift-mobility.
Amorphous Silicon Based Solar Cells, Xunming Deng, Eric A. Schiff
Amorphous Silicon Based Solar Cells, Xunming Deng, Eric A. Schiff
Physics - All Scholarship
Crystalline semiconductors are very well known, including silicon (the basis of the integrated circuits used in modern electronics), Ge (the material of the first transistor), GaAs and the other III-V compounds (the basis for many light emitters), and CdS (often used as a light sensor). In crystals, the atoms are arranged in near-perfect, regular arrays or lattices. Of course, the lattice must be consistent with the underlying chemical bonding properties of the atoms. For example, a silicon atom forms four covalent bonds to neighboring atoms arranged symmetrically about it. This “tetrahedral” configuration is perfectly maintained in the “diamond” lattice of …
Infrared Charge-Modulation Spectroscopy Of Defects In Phosphorus Doped Amorphous Silicon, Kai Zhu, Eric A. Schiff, G. Ganguly
Infrared Charge-Modulation Spectroscopy Of Defects In Phosphorus Doped Amorphous Silicon, Kai Zhu, Eric A. Schiff, G. Ganguly
Physics - All Scholarship
We present infrared charge-modulation absorption spectra on phosphorus-doped amorphous silicon (a-Si:H:P) with doping levels between 0.17% - 5%. At higher doping levels (1% - 5%) we find a sharp spectral line near 0.75 eV with a width of 0.1 eV. We attribute this line to the internal optical transitions of a complex incorporating four fold coordinated phosphorus and a dangling bond. This line is barely detectable in samples with lower doping levels (below 1%). In these samples a much broader line dominates the spectrum that we attribute to uncomplexed dopants. The relative strength of the two spectral features is in …
Thermionic Emission Model For Interface Effects On The Open-Circuit Voltage Of Amorphous Silicon Based Solar Cells, Eric A. Schiff
Thermionic Emission Model For Interface Effects On The Open-Circuit Voltage Of Amorphous Silicon Based Solar Cells, Eric A. Schiff
Physics - All Scholarship
We present computer modeling for effects of the p/i interface upon the open-circuit voltage VOC in amorphous silicon based pin solar cells. We show that the modeling is consistent with measurements on the intensitydependence for the interface effect, and we present an interpretation for the modeling based on thermionic emission of electrons over the electrostatic barrier at the p/i interface. We present additional modeling of the relation of VOC with the intrinsic layer bandgap EG. The experimental correlation for optimized cells is VOC = (EG/e)-0.79. The correlation is simply explained if VOC in these cells is determined by the intrinsic …
Chemical Vapor Deposited Amorphous Silicon For Use In Photothermal Conversion, David D. Allred, D. C. Booth, M. Janai, G. Weiser, B. O. Seraphin
Chemical Vapor Deposited Amorphous Silicon For Use In Photothermal Conversion, David D. Allred, D. C. Booth, M. Janai, G. Weiser, B. O. Seraphin
Faculty Publications
Efficient photothermal conversion requires surfaces of high solar absorptance and low thermal emittance. This can be accomplished by the tandem action of a good infrared reflector overlaid by a film of sufficient solar absorptance that is transparent in the infrared. Crystalline silicon is a suitable candidate for the absorber layer. Its indirect band gap, however, results in a shallow absorption edge that extends to far into the visible. In contrast, the absorption edge of amorphous silicon is steeper and located farther into the infrared, resulting in a larger solar absorptance. We report on the fabrication of amorphous silicon absorbers by …
The Use Of Nuclear Reactions And Sims For Quantitative Depth Profiling Of Hydrogen In Amorphous Silicon, David D. Allred, G. J. Clark, C. W. White, B. R. Appleton, C. W. Magee, D. E. Carlson
The Use Of Nuclear Reactions And Sims For Quantitative Depth Profiling Of Hydrogen In Amorphous Silicon, David D. Allred, G. J. Clark, C. W. White, B. R. Appleton, C. W. Magee, D. E. Carlson
Faculty Publications
Depth profiles for hydrogen in amorphous silicon have been determined by the use of resonant nuclear reactions [1H(15N,αγ)12C and 1H(19F,αγ)16O] and by secondary ion mass spectroscopy (SIMS). Independent calibration procedures were used for the two techniques. Measurements were made on the same amorphous silicon film to provide a direct comparison of the two hydrogen analysis techniques. The hydrogen concentration in the bulk of the film was determined to be about 9 at % H. The SIMS results agree with the resonant nuclear reaction results to within 10%, which demonstrates that quantitative hydrogen depth profiles can be obtained by SIMS analysis …