## 3 Results and Discussion
The result allows us to infer that the gradual current decrease after the peak current in the pristine P3 HT is due to the isotropic nature of the polymer chains in the solvent in comparison with the sonicated P3 HT solution. In other words, randomly oriented P3 HT chains in the pristine solution are not significantly influenced by a fast solidification process in which the abrupt P3 HT concentration increase, immobilizing the P3 HT polymer chains. In contrast, for the sonicated P3 HT chains with anisotropic ordering in solution, the abrupt solvent depletion leads to a significant reduction in the mobility of the polymer chains, suppressing the self-assembly driven by the interactions between the polymer chains in solution. In the pristine P3 HT, the effect of P3 HT chain mobility on ordering with further evaporation is not significant because the P3 HT chains are already entangled, resulting in randomly oriented polymer chains in the pristine P3 HT, which are not sensitive to the change in the concentration of P3 HT solution. To articulate the mechanism, however, further controlled experiments are required. To provide insights into channel formation mechanism, the use of a high boiling point solvent such as 1,2,4-trichlorobenzene (TCB) benefits in probing polymer conformation in-situ during solvent  
Figure 5: Plot of P3 HT four-point mobility as a function of P3 HT concentration of sonicated P3 HT solution. The inset shows a four-point geometry gated-device (L = 200 \(\upmu\)m, W = 2800 \(\upmu\)m d\({}_{\
u}\) = 80 \(\upmu\)m, and V\({}_{\text{diff}}\) = V\({}_{1}-\)V\({}_{2}\)). evaporation over the extended time. As seen in the Supporting Information, Figure S2, phase transition into the crystalline state is observed after an elapsed time following the current onset. The abrupt current onset in the initial stage results mainly from the formation of the conducting pathways, not by the phase transition from a non-crystalline to a crystalline phase. Comparing the magnitude of the current for both samples in Figure 3 with a lower boing point solvent (CHCl3), we observed a far larger current in the sonicated P3 HT from the current onset, as seen in Figure 3d. This clearly explains that anisotropic self-assembly in the sonicated P3 HT is retained during electrical channel formation, supporting that the source-drain current in the sonicated P3 HT evolves with the change in the degree of anisotropic ordering in the P3 HT solution. It is important to note that a possible current decrease due to doping in the Ar-filled glove box is excluded through comparison with that in air, in which the same trend was observed. Retention of anisotropic phase in solution into the ordered film phase is often suppressed by many factors, such as molecular weight, the choice of solvent, polymer regioregularity, concentration, and interaction with substrate. As found in earlier experiments, indeed, the FET mobility in the sonicated P3 HT is maximized at a narrow concentration range, evidencing that retention of a solution phase into a film phase involves many complicating factors. However, the far higher current observed during channel formation in the sonicated P3 HT, whether in solution state or in film state, points out that aggregated P3 HT clusters formed nano-crystallites both in the sonicated P3 HT solution and solid film phase, dominating other factors in determining the film structure, and thereby the magnitude of the electrical current. Given that sonication-induced ordering effect is more effective to regioregular P3 HT chains than regiorandom P3 HT chains [9; 22], ultrasonic irradiation is believed to act on facile formation of nano-crystallites by enhanced side-chain interactions between P3 HT molecules. To summarize, we found that enhanced anisotropic self-assembly of the P3 HT chains in solution acquired by sonication leads to the distinctly different temporal evolution of the electrical current, which is distinguished from that of the entangled pristine P3 HT chains.