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 ${\mathrm{O}}_2$ 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, $0.33–0.40\mathrm{eV}$ above the valence-band maximum. In contrast to ${\mathrm{O}}_2$, ${\mathrm{H}}_2\mathrm{O}$ molecules stay preferably intact between layers.

• Received 10 January 2007

DOI:https://doi.org/10.1103/PhysRevB.75.153202