Analysis of thin film polycrystalline heterojunction solar cells explains how minority carrier recombination at the metallurgical interface and at grain boundaries can be greatly reduced by the proper doping of the window and absorber layers. When this is done, these devices exhibit the high quantum efficiencies andJsc’s measured in high efficiency CdTe and CuInSe2based solar cells. The analysis also shows that any quantitative modeling of these devices which relates the device performance to the bulk electronic properties of the material must consider the additional geometric dimension introduced by the polycrystallinity. Additional analysis and measurements show that the present solar cells are limited by the magnitude of the diode current which appears to be caused by recombination in the space charge region.