We examine charge transfer between graphene and molecular semiconductors, parahexaphenyl and C60. Through in situ measurements of the current, we directly probe the charge transfer as the interfacial dipole is formed. We demonstrate that adsorbed molecules do not affect electron scattering rates in graphene. However, the molecules introduce p-type doping with only about one thousandth of an electron transferred per molecule [1].
Further, we investigate the growth of an oligoacene derivate dihydrotetraazaheptacene (DHTA7), which – due to nitrogen containing groups – forms solids through H-bonding and dipolar interactions between neighboring molecules. As a result of H-bonding networks, molecules form in-plane rows with subsequent layers exhibiting  stacking. Substrate-mediated self-assembled elongated molecular fibers of DHTA7 were grown by hot wall epitaxy on the surfaces of graphene and hexagonal boron nitride, which act as van der Waals electrodes and gate dielectrics. Using photo-assisted electrostatic force microscopy we demonstrate charge trapping and light-assisted charge spreading within the networks of DHTA7 fibers. We show that in the dark these fibers are not conductive, while visible light linearly polarized parallel to the long axis of the fibers allows spreading of the charges across the fiber network for tens of micrometers. Results indicate that – due to the inverse population created by the laser – charges that were trapped in the localized defects can spread through the bands of the fibers.