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Cz-silicon wafers in solar cell production: Efficiency-limiting defects and material quality control

 
: Haunschild, J.; Broisch, J.; Reis, I.; Rein, S.

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Fulltext urn:nbn:de:0011-n-2038098 (591 KByte PDF)
MD5 Fingerprint: 2ca8316fdba8b45d1c49c3ec8a63cb72
Created on: 6.6.2012


Photovoltaics International 15 (2012), pp.40-46
ISSN: 1757-1197
English
Journal Article, Electronic Publication
Fraunhofer ISE ()
PV Produktionstechnologie und Qualitätssicherung; Silicium-Photovoltaik; Charakterisierung; Qualitätssicherung und Messtechnikentwicklung: Material; Zellen und Module

Abstract
Most high-efficiency solar cells are fabricated from monocrystalline Czochralski silicon (Cz-Si) wafers because the material quality is higher than multicrystalline silicon (mc-Si) wafers. However, the material study presented in this paper reveals strong variations in the material quality of commercially available Cz-Si wafers, leading to a loss in solar cell efficiency of 4% absolute. The reason for this is the presence of defects, which appear as dark rings in photoluminescence (PL) images of the finished solar cells. It is shown that these efficiency-limiting defects originate from oxygen precipitation during emitter diffusion. It is demonstrated that an incoming inspection in the as-cut state is difficult, as strong ring structures in as-cut wafers turn out to originate most often from thermal donors. These are dissolved during high-temperature treatments and are therefore harmless, whereas moderate ring structures in the as-cut state may become severe. That is why critical wafers can be identified and sorted out reliably only after emitter diffusion, by using QSSPC-based lifetime measurements or PL imaging. The two-year statistics gathered from the research line at Fraunhofer ISE on the occurrence of ring defects in Cz-Si wafers indicate that ring defects are highly relevant in terms of material yield.

: http://publica.fraunhofer.de/documents/N-203809.html