We show that the electron mobility in films based on different derivatives of the ITIC family (ITIC, ITIC-Th and ITIC-4F) is strongly influenced by polymorphism; polymorphism specific to each molecule and depending on the annealing temperature applied to thin films. This leads to a strong increase in electron mobility compared to un-annealed films, which correlates with changes in molecular aggregation, crystallinity and domain orientation as well as intermolecular electronic coupling. Compared to the alkyl chain substitution used in ITIC-Th, fluorination in ITIC-4F leads to the highest electron mobility with 3.7×10-2 cm2/V.s at 200°C, due to the formation of highly ordered J-aggregates with enhanced intermolecular interaction.