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Effect of metal-wrap-through holes and etching parameters on the strength of multicrystalline silicon wafers

: Oswald, M.; Loewenstein, T.; Schubert, G.; Schoenfelder, S.

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Institut National de L'Energie Solaire -INES-:
6th International Workshop on Crystalline Silicon for Solar Cells, CSSC 2012 : October 8-11, 2012, Aix-les-Bains, France
Aix-les-Bains, 2012
4 pp.
International Workshop on Crystalline Silicon Solar Cells (CSSC) <6, 2012, Aix-les-Bains>
Conference Paper, Electronic Publication
Fraunhofer CSP ()
multicrystalline silicon; wafer; MWT; EWT; strength; laser; etching; micro structural analyses; mechanical bending test

Especially for wafers used in photovoltaic industry, defects from sawing damage, such as micro cracks, have significant influence on the strength of wafers. This is the reason why it is substantial to know what happens if additional defects are introduced artificially. Particularly, for solar cell concepts like Metal-Wrap-Through cells (MWT) or Emitter-Wrap-Through (EWT), the influence of laser drilled holes on the mechanical strength requires to be investigated. For this purpose, a laser was used to drill holes of 100 μm in diameter through the whole depth of multicrystalline wafers. After laser drilling, the batches were treated by isotropic etching, in order to remove laser induced damage. The strength behavior of each batch was determined by mechanical four-point-bending tests and statistical evaluation using Weibull distribution. The results show a significant decrease of strength with an increasing amount of laser holes, which, on the one hand, can be explained by the size effect of strength. On the other hand, micro structural analyses show that defects remaining from isotropic etching additionally reduce the strength of multicrystalline wafers.