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

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)