Classification of Pre-Breakdown Phenomena in Multicrystalline Silicon Solar Cells

Abstract

Pre-breakdown mechanisms in semiconductor s exhibit characteristic temperature dependences. Using temperature-dependent lock-in thermography (LIT) measurements and electroluminescence imaging under reverse bias we have found local regions with positive and with negative temperature coefficient (TC) of the breakdown current of multicrystalline silicon solar cells. In some regions, the temperature coefficient changes sign (from negative to positive) when going to higher temperatures. At low temperatures and for moderate reverse voltages, most pre-breakdown sites show a negative temperature coefficient, whereas the total cell current increases with temperature. This contradiction is resolved by rescaling the LIT images revealing that in the whole area of the cell a homogeneous reverse current flows, which increases with temperature and thereby compensates the negative TC of the localized currents. Altogether, in addition to the hard pre-breakdown (type III), the recombination-active defect-related soft pre-breakdown (type II) and the early pre-breakdown (type I), two additional pre-breakdown phenomena have been identified.