Estimation of diffusion lengths in CuInSe2-based cells using the photocurrent-capacitance method

Measurements have been made on CIGS cells from ZSW, Germany to estimate minority diffusion lengths (L_n) using the photocurrent-capacitance method. An XY recorder was employed in the place of the earlier point-by-point method to measure dark and illuminated current with variation of reverse voltage to minimize drift effects. However, the obtained L_n-values on the same cell had a wider spread of values than usual, with magnitudes too large to be acceptable. Nevertheless, it was found that preexposure of the cell to the light used during the measurements had a stabilizing effect on the variation of dark current with reverse bias. As a result, part of the variation of the illuminated-to-dark current change with reciprocal capacitance was made more reproducible. Using different optical filters on light pre-soaked CIGS cells, Ln was estimated to be about 2.5 μm ±40%.