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Cuevas A.,Australian NationalUniversity
IEEE Journal of Photovoltaics | Year: 2012

The analysis of solar cells where the posterior metal contact is formed only on part of the rear surface, which is mostly covered by a nonconductive, passivating layer, is both important and complex. A possible approach, based on a geometrical representation of the device structure, is examined here. As minority carriers flow toward the localized rear contact, they crowd inside a diminishing cross-sectional area, resulting in a high current density. The latter demands a strong gradient in their concentration, which leads to an increase of the open-circuit voltage V oc. Similarly, the crowding of majority carriers requires a strong gradient of the electrostatic potential, which leads to an increased series resistance R s. These effects of carrier crowding are described here with simple mathematical expressions that permit an approximate evaluation of V oc and R s for partial rear contact solar cells. © 2012 IEEE. Source


De Waele B.,SRK Consulting | De Waele B.,British Geological Survey | Thomas R.J.,British Geological Survey | Macey P.H.,Council for Geoscience | And 15 more authors.
Precambrian Research | Year: 2011

New detrital zircon U-Pb age data obtained from various quartzite units of three spatially separated supracrustal packages in central and northern Madagascar, show that these units were deposited between 1.8 and 0.8. Ga and have similar aged provenances. The distribution of detrital zircon ages indicates an overwhelming contribution of sources with ages between 2.5 and 1.8. Ga. Possible source rocks with an age of 2.5. Ga are present in abundance in the crustal segments (Antananarivo, Antongil and Masora Domains) either side of a purported Neoproterozoic suture (" Betsimisaraka Suture Zone"). Recently, possible source rocks for the 1.8. Ga age peak have been recognised in southern Madagascar. All three supracrustal successions, as well as the Archaean blocks onto which they were emplaced, are intruded by mid-Neoproterozoic magmatic suites placing a minimum age on their deposition. The similarities in detrital pattern, maximum and minimum age of deposition in the three successions, lend some support to a model in which all of Madagascar's Archaean blocks form a coherent crustal entity (the Greater Dharwar Craton), rather than an amalgamate of disparate crustal blocks brought together only during Neoproterozoic convergence. However, potential source terranes exist outside Madagascar and on either side of the Neoproterozoic sutures, so that a model including a Neoproterozoic suture in Madagascar cannot be dispelled outright. © 2011 Elsevier B.V. Source


Sharma N.,Australian NationalUniversity | Sharma N.,Australian National University | Gedeon T.D.,Australian NationalUniversity | Mendis B.S.U.,Australian NationalUniversity
Intelligent Decision Technologies | Year: 2013

The examination timetabling problem (ETP) is a NP complete, combinatorial optimization problem. Intuitively, use of properties such as patterns or clusters in the data suggests possible improvements in the performance and quality of timetabling. This paper investigates whether the use of a genetic algorithm (GA) informed by patterns extracted from student timetable data to solve ETPs can produce better quality solutions. The data patterns were captured in clusters, which then were used to generate the initial population and evaluate fitness of individuals. The proposed techniques were compared with a traditional GA and popular techniques on widely used benchmark problems, and a local data set, the Australian National University (ANU) ETP, which was the motivating problem for this work. A formal definition of the ANU ETP is also proposed. Results show techniques using cluster patterns produced better results than the traditional GA with statistical significance of p < 0.01, showing strong evidence. Our techniques either clearly outperformed or performed well compared to the best known techniques in the literature and produced a better timetable than the manually constructed timetable used by ANU, both in terms of quality and execution time. In this work, we also propose clear criteria for specifying the top results in this area. © 2013-IOS Press and the authors. All rights reserved. Source


Liang W.,Australian NationalUniversity | Weber K.J.,Australian NationalUniversity | Thomson A.F.,Australian NationalUniversity
IEEE Journal of Photovoltaics | Year: 2014

Passivation of p+ regions is typically achieved by Al2O3 layers with thicknesses in excess of 10 nm. Given the expense of commonly used Al2O3 precursors and, in some cases, the deposition time, it is desirable to minimize the layer thickness. We achieve recombination factor J+ in the order of 22 fA/cm2 with 1 nm of Al2O3 capped with ∼ 70-nm amorphous silicon nitride (SiNx:H) films on 85 Ω/□ boron diffusions. The passivation performance of ultrathin-Al2O3/SiNx:H stacks depends critically on both the alumina thickness and the SiNx:H composition. It was found that to achieve low J0p+ with 1-nm-Al2O3/SiNx:H stacks, the SiNx:H hydrogen concentration ([Si-H]+[N-H]) was required to be low: less than 8 × 1021 cm. Fourier transform infrared measurements indicated that the initial hydrogen content is more appropriate to evaluate the hydrogen release process of SiNx :H layers than Si-N bond density, at least in this study. Both the Al2O3-Si interface and charge density of 1-nm-Al2O3/SiNx:H stacks can be impacted by the SiNx:H capping layer. The outstanding passivation quality of 1-nm-Al2O3/SiNx:H stacks is due to a combination of both chemical and electrostatic passivation. © 2014 IEEE. Source

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