Highly efficient, large area polycrystalline silicon solar cells have been fabricated using ion implantation as a hydrogen passivation technique. A new high-current ion implanter with a bucket-type ion source has been developed to hydrogenate crystal defects in cast polycrystalline cells. Effective hydrogen passivation of the defects has been realized by implanting hydrogen ions into cast cells from the back surfaces and increasing the hydrogen ion energy and dose. A scanning light beam-induced current image of the polycrystalline cells shows that lowering of the induced current distribution at linear grain boundaries is almost completely eliminated, but not at irregular grain boundaries. The resultant polycrystalline cells exhibit a high conversion efficiency of 15.2% for a large area of 100 cm2.