Intercalation of oxygen and water molecules in pentacene crystals: First-principles calculations

Defect formation processes in semiconductors play an important role in controlling structural, electronic and transport properties. Here, we report the results of first-principles calculations of defect formation by oxygen and water molecules in a pentacene (Pn) molecular crystal, a prototypical system in organic electronics. We find that for both species, it is energetically favorable to enter Pn. The most stable defect structures resulting from O-2 intercalation and dissociation are either O complexes or single-O configurations. A special case is an intermolecular O bridge with levels in the energy gap of Pn, 0.33-0.40 eV above the valence-band maximum. In contrast to O-2, H2O molecules stay preferably intact between layers.