Rubrene crystal packing

FIGURE 2.1.15 Packing of molecules in rubrene crystals. The crystal facets used for the FET fabrication correspond to the a-b crystallographic plane the largest p is observed for the charge transport along the b axis. (From Sundar V. C. et al., Science, 303, 1644, 2004.)... 

The observed anisotropy of p in rubrene can be explained qualitatively on the basis of the molecular packing in these crystals (Figure 2.1.15). Due to the cofacial orientation of molecules in the stacks along the b axis, the charge motion along the stacks is facilitated in comparison with that in the perpendicular direction. Recent calculations of the band structure of rubrene based on the methods of quantum chemistry confirmed that the value of transfer integrals reaches a maximum for the b axis [17]. For the quantitative description of the mobility anisotropy and its... 

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