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Taking monocrystalline silicon to the ultimate lifetime limit

: Niewelt, Tim; Richter, Armin; Kho, T.C.; Grant, N.E.; Bonilla, R.S.; Steinhauser, Bernd; Polzin, Jana-Isabelle; Feldmann, Frank; Hermle, Martin; Murphy, J.D.; Phang, S.P.; Kwapil, Wolfram; Schubert, Martin C.

Volltext urn:nbn:de:0011-n-5040257 (2.2 MByte PDF)
MD5 Fingerprint: 57ac8d7b82ddb2d2ceed8072af1dd6c6
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Erstellt am: 21.8.2018

Solar energy materials and solar cells 185 (2018), S.252-259
ISSN: 0927-0248
Bundesministerium für Bildung und Forschung BMBF
01DR17019; CCPV
Zeitschriftenaufsatz, Elektronische Publikation
Fraunhofer ISE ()
Photovoltaik; Silicium-Photovoltaik; Charakterisierung von Prozess- und Silicium-Materialien; carrier lifetime; FZ-Silicon; passivation; record

A central quantity to assess the high quality of monocrystalline silicon (on scales beyond mere purity) is the minority charge carrier lifetime. We demonstrate that the lifetime in high purity float zone material can be improved beyond existing observations, thanks to a deeper understanding of grown-in defects and how they can be permanently annihilated. In a first step we investigate the influence of several process sequences on the lifetime by applying a low temperature superacid passivation treatment. We find that a pre-treatment consisting of an oxidation at 1050 °C followed by a POCl3 diffusion at 900 °C can improve the lifetime by deactivating or eliminating grown-in defects. Then, pre-treated wafers of different float zone materials are passivated with three state-of-the-art layer stacks. Very high effective lifetime values are measured, thereby demonstrating the high quality of the surface passivation schemes and the pre-treated silicon wafers. The measured effective lifetimes exceed previous records, and we report an effective lifetime of 225 ms measured on a 200 µm thick 100 Ω cm n-type silicon wafer symmetrically passivated with a layer stack of a thin thermally grown oxide and a polycrystalline layer (the TOPCon layer stack).