## 3 Results and Discussion
In other words, optimum P3 HT concentration for the formation of the efficient electronic transport pathways exists during solvent evaporation in which P3 HT solution concentration increases with time. The disentangled P3 HT chains in the sonicated P3 HT solution is more sensitive to solvent evaporation than the pristine P3 HT with entangled chains, leading to more orientational change than in the pristine P3 HT, causing a sharp peak current in comparison with a less sharp peak current in the pristine P3 HT, as seen in Figure 3b,c. As solvent drying proceeds with an increase in the P3 HT concentration, the distance between P3 HT chains become closer. The subsequent solvent evaporation varies the extent of anisotropic molecular self-assembly of the disentangled P3 HT molecules. According to [PERSON] et al., sonicated P3 HT back-bones interact in solution, leading to phase transition from the isotropic to the liquid crystalline phase [23]. From Raman spectroscopy data, C=C stretching peak frequency in the thiophene rings was varied during solvent evaporation, accounting for the fact that P3 HT back-bones interact with each other. Angular-dependent Raman intensities indicate that the P3 HT chains feature anisotropic ordering during solvent evaporation. For the sonicated P3 HT solution, as the concentration increases with further evaporation, anisotropic ordering is suppressed with more entangled P3 HT chains. To demonstrate the proposed hypothesis, we carried out experiments in which FET mobilities were measured as a function of P3 HT concentration in Figure 5. We observed that the mobility increased until a particular concentration followed by a decrease with a further increase in the concentration of the sonicated P3 HT solution. The presence of a peak FET mobility was reproducibly observed in several experiments. This clearly indicates that an optimum distance between P3 HT chains set by the  
Figure 4: Comparison of optical absorbance between the pristine and the sonicated P3 HT for (**a**) solution (5 mg/mL in CHCl\({}_{3}\)) and (**b**) film states (90 nm). concentration of the P3 HT solution exists in attaining the efficient electrical current path. In the case of the pristine P3 HT, P3 HT solution concentration-dependent FET mobilities were not observed. In other words, for the pristine P3 HT, change in the molecular orientation during solvent evaporation has a negligible effect on the source-drain current because the entangled P3 HT chains are randomly oriented, forming the disordered region. The abrupt current increase until saturation in the pristine P3 HT in Figure 3b is mainly, therefore, due to the increase in the P3 HT chain density with solvent evaporation rather than the increase in molecular ordering, as demonstrated in a far lower drain current than that in the sonicated P3 HT during channel formation, as observed in Figure 3d. The degree of ordering in the randomly oriented P3 HT chains in the pristine P3 HT solution state is not sensitive to further solvent evaporation, i.e., increase in the concentration, as supported by the little change in the drain current. The change in the current after the peak current in the sonicated P3 HT solution is associated with self-assembly of the polymer chains through a modified in-situ experiment. We tilted the substrate on which the source and drain contacts are patterned, as shown in the Supporting Information, Figure S1, to accelerate the elimination of the solvent in the channel region during the solidification process. For the sonicated P3 HT, the current drop after the peak current was not significant, which is similar to that in the pristine P3 HT. The absence of a dramatic current change indicates that abrupt immobilization of polymer chains by fast evaporation of solvent freezes the polymer chains, causing saturation of the current independent of pristine and sonicated P3 HT.