  The electronic properties of polycrystalline lead oxide consisting of a
network of single-crystalline $\alpha$-PbO platelets and the formation of the
native point defects in $\alpha$-PbO crystal lattice are studied using first
principles calculations. The $\alpha$-PbO lattice consists of coupled layers
interaction between which is too low to produce high efficiency interlayer
charge transfer. In practice, the polycrystalline nature of $\alpha$-PbO causes
the formation of lattice defects in such a high concentration that
defect-related conductivity becomes the dominant factor in the interlayer
charge transition. We found that the formation energy for the O vacancies is
low, such vacancies are occupied by two electrons in the zero charge state and
tend to donate their electrons to the Pb vacancies that leads to ionization of
both vacancies.The vacancies introduce localized states in the band gap which
can affect charge transport. The 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. Charge de-trapping from O vacancies can be accounted for the
experimentally found dark current decay in ITO/PbO/Au structures.
