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Stuttgart, Germany

Buchwald R.,Fraunhofer THM | Frohlich K.,Fraunhofer THM | Wurzner S.,Fraunhofer THM | Lehmann T.,Fraunhofer THM | And 2 more authors.
Energy Procedia | Year: 2013

The usage of diamond-plated wire to produce silicon wafers for the photovoltaic industry is still a new and highly investigated wafering technology. The requirements regarding the quality of the wafer surface are very high and they have to compete with the cost effectiveness and quality of wafers produced by the established loose abrasive sawing technology. Hence, the wafer topography, the fracture stress and the corresponding sub-surface damage have to be investigated and improved. This paper discusses the topographic parameters, the crack depths and the fracture stress of mono- and multi-crystalline silicon wafers that were produced on multi-wire saws using diamond-plated wire and comparable process parameters. Especially multi-crystalline silicon (mc-Si) wafers exhibit lower fracture stress values compared to mono-crystalline silicon (cz-Si) wafers. We investigated the relations between crack depth and fracture stress. In detail, we determined a 15% higher median and a 40% increased interquartile range of the crack depth of mc-Si wafers in comparison to similar produced cz-Si wafers. That correlates with lower fracture stress values of textured mc-Si wafers compared to cz-Si wafers. In the following, we studied the sub-surface damage as a function of crystal orientation in detail. It was found that the crack depths increases from the {100} plane over the {111} plane to the {101} plane. However for the {101} plane two grains were investigated, resulting in a discrepancy of 4 μm. This may be related to the unknown rotation angle between the corresponding {111} cleavage planes and the wire direction and requires further investigations. © 2013 The Authors.

Richter S.,Fraunhofer Center for Silicon Photovoltaics | Werner M.,Fraunhofer Center for Silicon Photovoltaics | Schley M.,PV Crystalox Solar Silicon GmbH | Schaaff F.,PV Crystalox Solar Silicon GmbH | And 6 more authors.
Energy Procedia | Year: 2013

The optimization of the float zone process for industrial application is a promising way to crystallize high purity silicon for high efficiency solar cells with reduced process costs. We investigated two differently produced Siemens rods which should be used as feed material for the float zone process. The aim is to identify and to improve material properties of the feed rods which have a high impact to the float zone process. We show here microstructural and chemical analysis comparing feed rods manufactured under standard conditions and under float zone adapted conditions. To resolve the growth behavior of the grains SEM/EBSD mappings are performed at different positions. TEM analyses are used to investigate the interface region between the mono- and the multicrystalline silicon within the Siemens feed rod. Additionally, drilled cores are cut out from the feed rods containing the region of the slim rod. Afterwards, the drilled cores are crystallized with the float zone process. Finally, carbon and oxygen measurements with FT-IR spectrometry on different positions of the crystallized drilled cores of the Siemens feed rods show the influence of the slim rod material to the float zone process. © 2013 The Authors.

Anspach O.,PV Crystalox Solar Silicon GmbH | Hurka B.,PV Crystalox Solar Silicon GmbH | Sunder K.,PV Crystalox Solar Silicon GmbH
Solar Energy Materials and Solar Cells | Year: 2014

This work presents the evolution from fundamental single wire sawing experiments using structured wire for the first time to the introduction of this wire in multi-crystalline silicon wafer mass production. It is shown that via single wire experiments 100% higher throughput and more than 10% less specific energy consumption were foreseen for the replacement of straight with structured wire in mass production of multi-crystalline silicon wafers. The analysis of production data demonstrates that these predictions were even exceeded and that additionally, 45% less wire consumption and 40% less slurry consumption were achieved. This work reveals the influence on wafer metrology and gives a basic description of the dynamics in the cutting slot. © 2014 Elsevier B.V.

Meissner D.,PV Crystalox Solar Silicon GmbH | Schoenfelder S.,Fraunhofer Center for Silicon Photovoltaics | Hurka B.,PV Crystalox Solar Silicon GmbH | Zeh J.,PV Crystalox Solar Silicon GmbH | And 8 more authors.
Solar Energy Materials and Solar Cells | Year: 2014

In the multi wire sawing process the wire tension is an important parameter for reliability and wafer quality. Changes of wire quality and wire tension from one end of a wire web in a multi wire saw to the other are investigated by several methods: wire tension measurements in the wire saw, wire elongation during an industrial process and material testing of representative wires. Two mechanisms for the loss of wire tension are identified. Firstly, the decrease of wire diameter due to abrasion causes a slow loss of wire tension along the whole wire web. Secondly, plastic deformation of the wire due to random overloading leads to a fast decrease of the wire tension within the first few centimeters of the wire web. Both effects are confirmed by modeling and calculations. © 2013 Elsevier B.V.

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