Low‐Temperature Saw Damage Gettering to Improve Minority Carrier Lifetime in Multicrystalline Silicon

• Published in: Physica status solidi. PSS-RRL. Rapid research letters 2017-10, Vol.11 (10), p.n/a
• Main Authors: Al‐Amin, M., Grant, N. E., Murphy, J. D.
• Format: Article
• Language: English
• Subjects: Carrier lifetime; Damage; Gettering; Impurities; Low temperature; minority carrier lifetime; Minority carriers; Photovoltaic cells; Polycrystals; Service life assessment; Silicon; Solar cells; Solid state physics
• ISSN: 1862-6254; 1862-6270
• DOI: 10.1002/pssr.201700268

The minority carrier lifetime in multicrystalline silicon − a material used in the majority of today's manufactured solar cells − is limited by defects within the material, including metallic impurities which are relatively mobile at low temperatures (≤700 °C). Addition of an optimised thermal process which can facilitate impurity diffusion to the saw damage at the wafer surfaces can result in permanent removal of the impurities when the saw damage is etched away. We demonstrate that this saw damage gettering is effective at 500 to 700 °C and, when combined with subsequent low‐temperature processing, lifetimes are improved by a factor of more than four relative to the as‐grown state. The simple method has the potential to be a low thermal budget process for the improvement of low‐lifetime “red zone” wafers. The authors demonstrate a novel low‐temperature (≤700 °C) process to improve carrier lifetime in multicrystalline silicon for photovoltaics. Surface damage created when ingots are cut into wafers is used as a gettering site for metallic impurities, thus enabling impurities to be easily removed from the wafer subsequently. A factor of >4 lifetime improvement is achieved, highlighting that saw damage gettering could be a low thermal budget process to improve poor quality silicon.