Numerical calculations have been made of the effect of grain size on the short-circuit current and the AM1 efficiency of polycrystalline thin film InP, GaAs, and Si Schottky barrier solar cells. Si cells 10 µm thick are at best 8 percent efficient for 100-µm grain sizes; 25-µm-thick Si cells can be about 10 percent efficient for this grain size. GaAs cells 2 µm thick can be 12 percent efficient for grain sizes of 3 µm or greater. © 1977 IEEE. All rights reserved.