In this work, P(NDI2OD-T2) was blended with various amounts of PEO, aPP, or iPP to furnish numerous thin films. The morphology of pristine P(NDI2OD-T2) and the blends was investigated by X-ray photoelectron spectroscopy, grazing-incidence X-ray scattering (GIXS), near-edge X-ray absorption fine structure spectroscopy, UV-vis spectroscopy, and atomic force microscopy, revealing that the aggregation of P(NDI2OD-T2) is adjustable, and the interconnected P(NDI2OD-T2) domain can be readily achieved. Furthermore, the transformation of P(NDI2OD-T2) from face-on to edge-on crystallites was observed at a specific blend. A rationale by adopting the geometric shape of crystallite is proposed to account for this transformation. P(NDI2OD-T2) and the blends were submitted to organic field-effect transistor fabrication in the bottom-gate/top-contact geometry. The relationship between the electron mobility and the GIXS morphological characteristics is established. According to the fitting equation, the pi stacking and polymer backbone of P(NDI2OD-T2) play significant roles in determining the electron mobility.