PACS 73.61. Ga, 81.15.Cd, 84.60.Jt Polycrystalline n-ZnO/p-Cu 2 O heterojunctions were fabricated by reactive sputtering for photovoltaic applications. Although electrical rectification was not reproducibly obtained in the as-grown samples, rectification was observed in the samples fabricated with cyanide treated Cu 2 O. We have previously shown that cyanide treatment has an effective role in passivation of defects in Cu 2 O, in analogy to hydrogen passivation. It is, therefore, believed that the observed improvement in the electrical rectification of the ZnO/Cu 2 O heterojunctions is attributable to the defect passivation near the hetero-interface. The effectiveness of the cyanide treatment and the importance of defect passivation in ZnO/Cu 2 O heterojunctions are presented.