A qualitative model describing grain‐boundary effects in polycrystalline heterostructure solar cells is presented. Two salient observations of the model are (1) that an accumulated grain boundary in the light‐absorbing layer can produce a surface field that serves to reduce grain‐boundary recombination and increase device short‐circuit current and (2) that the grain boundary in either the window layer or absorber layer should be depleted so as to avoid high device tunneling currents. Avoiding high tunneling currents leads to high device open‐circuit voltages. The model describes additional electrical effects and suggests means of controlling and characterizing grain‐boundary types.