[en] A diffusion theory of carrier transport across a grain-boundary barrier is used to study the influence of photoexcitation on the current-voltage characteristic of a bicrystal with n-type grains and acceptor surface states at the grain boundary. Possible generation of a photo-emf in such a bicrystal is investigated on the assumption that the rate of photogeneration of electron-hole pairs g₁ and the hole lifetime T₁ on one side of the grain boundary are generally different from the corresponding values of g₂ and T₂ on the other side. The results are given of a numerical calculation of the current-voltage characteristic of a wide-gap semiconductor bicrystal with different values of g₁, g₂, T₁, and T₂