In this work, we investigate the effect of pre-aggregated solutions of diketopyrrolopyrrole (DPP)-based conjugated polymers to achieve highly-aligned polymer films for high-performance organic field-effect transistors (OFETs). A suitable marginal solvent is selected for 5-octyl-pentadecyl branched DPP and selenophene-based semiconducting polymer (PDPP(SE)-epsilon-C8C15) by utilizing the Hansen solubility parameter calculation. The anisotropic one-dimensional aligned PDPP(SE)-epsilon-C8C15 film was off-center spin-coated from the pre-aggregated solution is studied by atomic force microscopy and polarized UV-Vis absorption spectroscopy. A significantly high hole mobility of 4.16 cm(2)V(-1)s(-1) was achieved from the OFETs with a unidirectionally-aligned PDPP(SE)-epsilon-C8C15 film to the transistor channel direction.