Diffusion length estimation in CuInSe 2-based cells by the photocurrent–capacitance method

Abstract

Using the photocurrent–capacitance method, measurements have been made on Cu(InGa)Se 2 (CIGS) cells from ZSW, Germany to estimate minority diffusion lengths ( L n). To minimize drift effects, an X– Y recorder was employed in the place of an earlier point-by-point method to measure dark and illuminated current with variation of reverse voltage. 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 pre-exposure 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, the middle range 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, L n was estimated to be approximately 2.5 μm ±40%.