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Konstanz, Germany

Urrejola E.,ISC Konstanz | Peter K.,Sunways AG | Plagwitz H.,Sunways AG | Schubert G.,Sunways AG
Applied Physics Letters | Year: 2011

We show that the lateral spread of silicon in a screen-printed aluminum layer increases by (1.50±0.06) μm/°C, when increasing the peak firing temperature within an industrially applicable range. In this way, the maximum spread limit of diffused silicon in aluminum is predictable and does not depend on the contact area size but on the firing temperature. Therefore, the geometry of the rear side pattern can influence not only series resistance losses within the solar cell but the process of contact formation itself. In addition, too fast cooling lead to Kirkendall void formations instead of an eutectic layer. © 2011 American Institute of Physics.

Lohmann M.,ISC Konstanz | Wefringhaus E.,ISC Konstanz
Energy Procedia | Year: 2013

In this paper, alkaline textured surfaces are described by means of statistical methods to evaluate what can be behind the term homogeneity found in literature. The evaluation of pyramid homogeneity is described in respect of the pyramid tip positions in the plane by testing against complete spatial randomness. The basic statistical methods used are described and a comparison with microscopic geometrical features of the pyramids is discussed. The statistical analysis yields appropriate classifications allowing for quantitative judgment of whether a surface has a regular (" homogeneous") distribution of pyramids or not. © 2013 The Authors.

Lippold M.,TU Bergakademie Freiberg | Buchholz F.,ISC Konstanz | Gondek C.,TU Bergakademie Freiberg | Honeit F.,TU Bergakademie Freiberg | And 2 more authors.
Solar Energy Materials and Solar Cells | Year: 2014

The reactivity of HF(40 wt%)-HNO3(100 wt%)-H2SO 4(97 wt%) etching mixtures towards conventional SiC-slurry and diamond-wire sawn silicon wafers has been studied. Sulfuric acid-rich mixtures exhibit adequate etching rates (r<5 μm min-1) and generate homogenously distributed, small etching pits on both types of silicon wafers. Textured wafer surfaces were characterized by means of scanning electron microscopy (SEM), laser scanning microscopy (LSM), surface roughness analyses and reflectivity studies. The surface roughness is influenced by the etch depth and the type of saw damage. Etching in sulfuric acid-rich mixtures significantly reduces the reflection of SiC-slurry sawn wafers and, in particular, of diamond-wire sawn wafers. The reflection of etched silicon surfaces is discussed in terms of etch depth and surface roughness. Compared to the conventional HF-HNO3-H2O etching process, multicrystalline silicon (SiC-slurry and diamond-wire sawn) based solar cells texturized by sulfuric acid-rich mixtures exhibit increased efficiencies. © 2014 Elsevier B.V.

Butler K.T.,University of Sheffield | Vullum P.E.,Sintef | Muggerud A.M.,Norwegian University of Science and Technology | Cabrera E.,ISC Konstanz | Harding J.H.,University of Sheffield
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We present the results of an experimental and atomistic modeling investigation of the silicon/silver (Si/Ag) interfaces found in industrial solar cells. We use small ab initio calculations to parametrize a new interatomic potential for the Si/Ag interaction. This interatomic potential is then validated against larger ab initio calculations as well as the results of previous experimental and theoretical studies of Si/Ag systems. The interatomic potential allows us to perform a large-scale search of the conformational space of Si/Ag interfaces identified from transmission electron microscopy studies. The most favorable geometries thus identified are then used as the input for more accurate ab initio calculations. We demonstrate that the two interfaces which we identify experimentally have significantly different geometric and electronic structures. We also demonstrate how these different structures result in significantly different Schottky barriers at the interfaces. © 2011 American Physical Society.

Wilson M.,Semilab SDI LLC | Edelman P.,Semilab SDI LLC | Lagowski J.,Semilab SDI LLC | Olibet S.,ISC Konstanz | Mihailetchi V.,ISC Konstanz
Solar Energy Materials and Solar Cells | Year: 2012

Excess carrier photoconductance decay lifetime, measured under small perturbation conditions imposed on steady-state generation, offers an attractive and parameter free alternative to quasi-steady-state photoconductance, QSSPC. A recent version of this technique referred to as QSS-μPCD is based on microwave reflectance PCD monitoring. For this technique, it is critically important to maintain a mono-exponential decay over a large range of steady-state light intensity. Toward that goal we present QSS-μPCD with stringent quality of decay control, QDC. The quality of decay parameter, QD (ideally QD=1) measures the direction and magnitude of departures from an ideal exponential transient and enables tuning toward an optimal range of experimental variables, both apparatus and wafer dependent, whereby QD is within 1±Δ where Δ defines the QDC limits. Within QDC limits, the small perturbation effective decay lifetime, τ eff.d, enables accurate determination of important silicon PV parameters, up to about 25 suns, including J 0 and the steady-state lifetime, τ eff.ss. Two J 0 procedures are compared. The ingenious analytical procedure adopted from Basore and Hansen (1990) [2] enables direct determination of J 0. The second J 0 procedure uses integration of τ eff.d over illumination intensity. The results are self-consistent and they show excellent correlation with Sinton QSSPC results. © 2012 Elsevier B.V. All rights reserved.

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