Analysis of the defect activation in Cz-silicon by temperature-dependent bias-induced degradation of solar cells

The activation of the metastable defect in boron-doped Cz-Si is analyzed by application of small forward voltages to Cz-Si cells in the dark. In contrast to the carrier injection by light used in previous experiments, this method allows to observe the defect activation at very low excess carrier densities. Thus, the minimum level of excess carriers necessary to activate the metastable defect could be determined for the first time. This threshold value was measured for materials with different boron concentrations at different temperatures. Our analysis allows to decide that the defect activation is not due to a shift of the Fermi-level across a certain defect energy level, changing its charge state, but due to a recombination-enhanced activation of the defect.