High mobility semiconducting polymers offer a concrete opportunity to develop flexible and large area electronics for a vast range of applications, including wearable, portable and distributed sensor, monitoring and actuating devices. A key role in the determination of the field effect mobility (ยต) is played by the morphology of the polymeric films, since the percolation path of the charge carriers in a Field Effect Transistor (FET) is sized by the micrometric length of the channel. The observation of transport anisotropy in the most promising semiconducting polymers is lately inspiring scientists to develop directional deposition methods, able to provide active phases with an efficient short-range inter-molecular packing as well as controlled directionality of the polymer backbones. Nevertheless, the possibility to integrate such requirements in low costs, large area production lines represents a real challenge. In this contribution we demonstrate that naphthalene-diimide based copolymers, when conveniently processed from solution, can self-organize in fibril-like supramolecular nanostructures where the polymer backbones arrange parallel to the fibril axis. Importantly, we found that such self-assembling properties give access to the realization of fast molecular alignments on large areas, simply exploiting and controlling the elongational flows occurring during the solution deposition. The chemical rationale behind these phenomena was investigated through the systematic substitution of the solubilizing branched side chains, which were found to be responsible for the self organization in solution of the polymer chains; thus, we were able to define the optimal chemical functionalities for this class of materials promoting a flow-induced alignment. Finally, basing on these findings, a neat molecular alignment on large area was demonstrated using a fast, scalable, low temperature and ambient-processed directional deposition methods such as bar coating. Electron mobility values parallel to the coating direction systematically overcome those perpendiculars of more than one order of magnitude, approaching 3 cm2/Vs, thus enabling operating frequencies of practical utility, i.e. above 1 MHz. By linking transport properties from the meso- to macro-scale, this work offers a critical perspective for controlling mobility in polymer FETs.