The electronic properties of polycrystalline lead oxide consisting of a network of single-crystalline α-PbO platelets and the formation of native point defects in the α-PbO crystal lattice are studied using first-principles calculations. The results suggest that the polycrystalline nature of α-PbO causes the formation of lattice defects (i.e., oxygen and lead vacancies) in such a high concentration that defect related conductivity becomes the dominant mechanism of charge transport. The neutral O vacancy forms a defect state at 1.03 eV above the valence band which can act as a deep trap for electrons, while the Pb vacancy forms a shallow trap for holes located just 0.1 eV above the valence band. The ionization of O vacancies can account for the experimentally found dark current decay in ITO/PbO/Au structures.