Charge transport in organic semiconductors is strongly dependent on their molecular packing modes in the solid state. Therefore, understanding the relationship between molecular packing and charge transport is imperative, both experimentally and theoretically. However, so far, the fundamental effects of solid-state packing and molecular interactions (e.g. NH⋅⋅⋅π) on charge transport need further elucidation. Herein, indolo[3,2-b]carbazole (ICZ) and a derivative thereof are used as examples to approach this scientific target. An interesting insight obtained thereby is that NH⋅⋅⋅π interactions among ICZ molecules facilitate charge transport for higher mobility. Subtle changes in the of NH⋅⋅⋅π interactions can significantly influence both the molecular packing and the charge-transport properties. Therefore, a method for exploiting intermolecular NH⋅⋅⋅π interactions would yield novel molecular systems with designable characteristics.