DEFECT CHARACTERIZATION IN AMORPHOUS-SILICON BASED SOLAR-CELLS BY SUBBAND-GAP SPECTROSCOPY WITH CONSTANT PHOTOCURRENT MEASUREMENTS

We used the constant photocurrent method to characterize a-Si:H based pin cells in order to discuss the correlation between the device characterizing quantity, the fill factor (FF), and the number of defects which is related to the quantity alpha-D (subbandgap optical absorption constant). We show that the changes in the i layer due to the creation of metastable defects after light soaking or current injection - characterized by alpha-D - directly correlate with the changes in solar cell performance (FF). We are able to show that other reasons than an increased defect density can lead to a reduction of the fill factor. Further we try to quantify alpha-D in terms of a defect density of states.