A theoretical analysis is made of the nonexponential current-voltage characteristics observed in Al-poly-Si (Wacker) Schottky-barrier solar cells fabricated in our laboratory. In this model, we consider a grain boundary effectively in parallel with the Schottky junction. Comparison between experimental data and numerical calculation indicates that the grain boundary may be represented by a fixed interface charge, a uniformly distributed interface state density, and a neutral level E0. Diodes fabricated in regions with high-angle grain boundaries behave in a manner which conforms closely with the proposed model.