Characterization of a-Si:H Based Pin Cells by Subbandgap Photocurrrent Spectroscopy

In a systematic study we measured the spectral distribution of the optical absorption coefficient α (h ν) within the subbandgap energy range. This was done by constant photocurrent method (CPM) measurements on glow-discharge deposited a-Si based pin cells. He evaluated typical CPM spectra for pin cells with thicknesses ranging from 0.4 µm to 10 µm. We discuss the correlation between the device characterizing quantity, the fill factor (FF), and the number of defects which is related to the quantity αD (subbandgap optical absorption constant). He show that the changes in the i-layer due to the creation of metastable defects after light soaking or current injection — characterized by αD — directly correlate with the changes in solar cell performance (FF). Further we try to quantify αD in terms of a defect density of states (DOS).