Hot spots in multicrystalline silicon solar cells: avalanche breakdown due to etch pits

• Published in: Physica status solidi. PSS-RRL. Rapid research letters 2009-03, Vol.3 (2-3), p.40-42
• Main Authors: Bauer, J., Wagner, J.-M., Lotnyk, A., Blumtritt, H., Lim, B., Schmidt, J., Breitenstein, O.
• Format: Article
• Language: English
• Subjects: 61.72.Lk; 68.37.Hk; 68.37.Lp; 77.22.Jp; 84.60.Jt
• ISSN: 1862-6254; 1862-6270
• DOI: 10.1002/pssr.200802250

Multicrystalline silicon solar cells typically show hard breakdown beginning from about –13 V bias, which leads to the well‐known hot‐spot problem. Using special lock‐in thermography techniques, hard breakdown has been found to occur in regions of avalanche multiplication. A systematic study of these regions by various electron microscopy techniques has shown that the avalanche breakdown occurs at cone‐shaped holes, located at dislocations and caused by acidic texture etch. At their bottom, these etch pits lead to a strongly curved p–n junction exhibiting an electrostatic tip effect which quantitatively explains the field enhancement needed for enabling avalanche breakdown. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) Hot spots in solar cells limit their usability since they lead to the destruction of the module. In this Letter the authors present a combined lock‐in thermography, lock‐in electron‐beam‐induced current, scanning and transmission electron microscopy investigation revealing hot spots in acidic‐textured multicrystalline Si cells as being due to etch pits.