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Iron Impurities in Wafers Based on Different So-G Silicon Feedstock |
Abstract/Summary: Iron is the dominant impurity in multicrystalline solar grade silicon (SoG-Si) produced by the Elkem Solar metallurgical method, and can be found in concentrations as large as 1014 -1015 atoms cm-3. The aim of the present investigation has been to reveal the chemical nature of iron and iron precipitates in Elkem Solar Silicon® (ESS™). The experimental approach which is used to characterize iron and its precipitates is based on a combination of several experimental techniques, such as microwave photoconductivity decay, secondary ion mass spectrometry, x-ray fluorescence, and transmission electron microscopy, which produce mutually complementary information. Wafers from two different Elkem Solar multicrystalline p-type feedstock, Elkem 1(simplified Elkem Solar process) and Elkem 2 (early plant start-up test production) where examined and compared to a reference multicrystalline p-type silicon from an external source. The average minority carrier lifetime of Elkem 1, 2.1 μs was significantly low compared to 28 μs for both Elkem 2 and reference. Fe-B pair concentration was higher in Elkem 1, and there is also suggested that Fe-Al and Fe-O pair concentrations were higher in Elkem 1. F-Al-O concentrations in clusters are higher in low minority carrier lifetime areas compared to high lifetime areas. Cluster containing these elements seems to have strong recombination strength. The concentration of clusters is higher in low lifetime areas. Clusters located in high lifetime areas are on the other hand much larger suggesting that the total content of Fe, Al and O to a higher degree should be located in the clusters and less as interstitial iron and iron precipitates. These forms of impurities can together make a large contribution to minority carrier lifetime and partly explain the low lifetime found in Elkem 1 wafers. |
| Author(s): |
E. Hvidsten Dahl, V. Osinniy, A. Nylandsted Larsen, R. Tronstad, P.H. Middleton, T.O. Sætre, K. Friestad |
|
| Keywords: |
Minority Carrier Lifetime, So-G Silicon, Iron Impurity, Iron Pair, Metallurgical Route |
|
| Topic: |
Wafer-Based Silicon Solar Cells and Materials Technology |
|
| Subtopic: | Silicon Feedstock, Crystallisation and Wafering | |
| Event: | 25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain | |
| Session: | 2CV.1.39 | |
| Pages: |
1571 - 1575 |
|
| ISBN: | 3-936338-26-4 | |
| DOI: | 10.4229/25thEUPVSEC2010-2CV.1.39 | |
| Price: |
0,00 EUR |
