Characterization of crystal polymorphs of the organic semiconductor non-peripheral octa-hexyl phthalocyanine

The carrier-transport and thermodynamic properties of two crystal polymorphs, i.e., bulk and needle polymorphs, of non-peripheral octa-hexyl substituted phthalocyanine were investigated using density functional theory calculations and molecular dynamics simulations. The calculated results show that the bulk and needle polymorphs have hole mobilities of the same order of magnitude and that the hole mobility of the bulk polymorph was approximately twice that of the needle polymorph. For ideal one-dimensional transport along π stacking columns, the difference in mobility between the two polymorphs was larger by a factor of approximately 8. Therefore, we can expect the bulk polymorph to have 2 (or 8) times higher mobility than the values for the needle polymorph. These results predict that the bulk polymorph has the potential to show higher device performance than the needle polymorph. We also obtained the results that imply that a needle-polymorph-like phase with uniform (monoclinic) phthalocyanine-core tilting (instead of the alternative tilting of the needle polymorph) could be a new polymorph in this crystal system.