Improvement in Diffusion Length Estimation using the Photocurrent-Capacitance Method in CuInSe2-based Cells

Abstract

ABSTRACTThe experimental technique in the photocurrent-capacitance method of estimating minority diffusion lengths, as applied to CuInSe2-based photovoltaic cells, has been improved, principally by replacing the earlier chopped light and monochromator technique by one employing a steady strong stable light source and a long pass optical filter. The filter requires an absorption edge at an appropriate wavelength to provide the penetrating light at sufficient intensity, which has been found to be 1.1 μm for CuInSe2 cells and 1.0 μ for Cu(In,Ga)Se2 cells. In addition, the parallel capacitance is determined with reverse bias under the same illumination as that during the photocurrent measurements and at a suitable frequency, such as 10 kHz. With these changes, the technique has been found to be more tolerant to cell imperfections and reproducible estimates of diffusion length have been obtained on CuInSe2 and Cu(In,Ga)Se2 cells.