Minority‐carrier diffusion has been investigated in as‐grown CdZnS/CuInSe2solar cells. Capacitance‐voltage (C‐V) and photoconductivity measurements are combined to determine diffusion and interface recombination processes. Diffusion lengths of about 2 &mgr;m and a small interface recombination velocity are determined from biased photoconductivity, biased spectral response, and photoluminescence studies. Photoluminescence studies also indicate that a much lower interface recombination velocity occurs at the CdZnS/CuInSe2interface than that at a bare CuInSe2surface.