Structural origin of a cluster of bright spots in reverse bias electroluminescence image of solar cells based on Si multicrystals

Electroluminescence (EL) imaging was utilized to investigate spatial distribution of electric properties of solar cells based on Si multicrystals with different base resistivity. A part of electrically active defects in solar cells, observed as dense dark lines In the EL image under the forward bias, was found to be detected as a cluster of bright spots in the EL image under the reverse bias especially when the base resistivity is low. This observation was accompanied with decrease in filling factor of solar cells. Local structural analysis clarified that sub-grain boundaries are responsible for the defects.