High vertical carrier mobilities in organic semiconductor films are a challenging issue for fundamentally improving the performance of vertical devices. To achieve improvement in the vertical direction, a reduced graphene oxide (rGO) template is used with pentacene and DNTT having a herringbone structure enabling two-dimensional (2D) transport in comparison with CuPc having a slipped-stack structure. A thin-film structure and the optoelectrical properties of the oriented films are investigated with respect to molecular structures and packing modes. The rGO template induces a "laid-down" herringbone structure for pentacene and DNTT with a face-on orientation. Our results reveal that intermolecular dispersion energy is an additional important factor to form face-on states of molecules and influences face-on ratios in the films on rGO. Vertical charge mobilities of the films are significantly enhanced by the rGO template. Particularly, the DNTT film with a laid-down herringbone structure produces a vertical mobility as high as 0.27 cm2 V-1 s-1, one of the highest values for ordinary thin films with several hundred nanometer thickness. These findings suggest that 2D transport is advantageous for vertical carrier transport also.
Keywords: charge mobility; molecular orientation; molecular packing; organic semiconductor; reduced graphene oxide.