An improved light‐beam‐induced current apparatus was used to evaluate grain‐boundary activity in a polycrystalline solar cell. The grain‐boundary recombination velocity and the diffusion length in the neighboring grains were obtained by processing of the grain‐boundary profiles. The technique was applied using various wavelengths in the 550–950 nm range to check the consistency of the method and to examine the depth profile of the parameters measured. The results show that the diffusion length measurement is independent of the wavelength, and that the measured grain‐boundary recombination velocity increases with the wavelength. The method was also used to evaluate hydrogen passivation of the grain boundary examined.