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Influence of crucible and coating on the contamination of directionally solidified silicon

First results of the german research network "SOLARWINS"
 
: Kwapil, W.

:

Nowak, S. ; European Commission:
27th European Photovoltaic Solar Energy Conference and Exhibition, EU PVSEC 2012. DVD-ROM : Proceedings of the international conference held in Frankfurt, Germany, 24 - 28 September 2012
München: WIP-Renewable Energies, 2012
ISBN: 3-936338-28-0
S.627- 635
European Photovoltaic Solar Energy Conference and Exhibition (EU PVSEC) <27, 2012, Frankfurt>
Englisch
Konferenzbeitrag
Fraunhofer CSP ()
coating; crystallisation; crystallization; multicrystalline silicon

Abstract
The German research network "SolarWinS", aiming at elucidating the fundamental limitation of multicrystalline silicon for solar cells, investigates the interaction between the silicon and its environment during solidification and cool-down. Ingots of format G1 were grown in standard industrial crucibles and in high-purity crucibles made from fused silica, both coated with the same standard industrial silicon nitride coating. The concentrations of many metallic elements are similar in both types of silicon blocks. Nevertheless, in comparison with the standard ingot, the carrier lifetime in the high-purity ingot is significantly higher and the low-lifetime edge region close to the crucible wall is smaller. These differences are attributed to the lower interstitial iron concentration in the high-purity ingot which is a result of the interaction between the crucible, the silicon nitride coating and the silicon: While the standard industrial crucible acts as an infinite Fe source, iron atoms can diffuse from the coating into the high-purity crucible due to the favorable concentration gradients. Therefore, the silicon nitride coating applied to the high-purity crucible acts as a depletable source for Fe. Modeling the iron distributions by two different solutions of the Fickian diffusion equation succeeds at reproducing the main features of the observed metal concentration distributions and carrier lifetime measurements.

: http://publica.fraunhofer.de/dokumente/N-236409.html