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Title:
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Kristallijn silicium zonnecellen: thermische behandelingen en nieuwe materialen - THERMAT II
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Author(s):
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Published by:
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Publication date:
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ECN
Solar Energy
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1-1-2005
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ECN report number:
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Document type:
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ECN-C--05-011
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ECN publication
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Number of pages:
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Full text:
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155
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Download PDF
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Abstract:
The TherMat II project investigated the relation between silicon materialquality and solar cell efficiency, and the changes in material which
occur as a result of high-temperature process steps. Goals of the project
were 1. to find out whether the negative effects of extra impurities
in the silicon wafer, e.g. due to the use of new feedstock, can be avoided.
2. to find out which extra impurities and defects are present in Si
wafers which are made with modern high-throughput equipment and prototypes,
and how these can be eliminated. 3. to look at the effect of short high-temperature
process steps. Important results of the project are - new quantitative
information on the presence of impurities, and new insight in the segregation
phenomena occurring during crystallisation of silicon (chapter 1). -
new knowledge on measuring Fe in silicon (chapters 2 and 3). - new insight
in the relation between the doping of the silicon and the detrimental
effect of impurities (chapters 4 and 5). - characterisation of the detrimental
effect of boron-oxygen defect-pairs (chapter 6). - promising results
to measure and characterise the passivation of defects with hydrogen,
by monitoring interstitial Fe (chapter 7). - insight in the relation
between ingot growth, Si material parameters and cell efficiency for
standard processing (chapters 8 and 9). - improved gettering of impurities
during emitter diffusion (chapter 10). Four practical results are particularly
noteworthy: - Improvement of the thermal profile for gettering/diffusion,
resulting in carrier lifetime increases of up to a factor 10; - Understanding
of the doping-dependence of carrier lifetime in Si, in particular leading
to a proposal to use n-type doping for future lower-quality Si wafers;
- Quantification of (part of) the detrimental effect of oxygen (due
to its interaction with boron) in mc-Si; and - Results which open the
way for a better characterisation of the passivation of defects with
hydrogen, by monitoring interstitial Fe.
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