## 3 Results and Discussion
The FET hole mobilities were extracted from the forward gate scan, which is scanned from the positive to the negative gate voltage. The magnitude of the drain current during solidification of the P3 HT solution in the channel region is governed by the formation of the conducting pathways, the degree of ordering, and the carrier concentration [26, 27, 28]. The magnitude of the maximum current in the sonicated P3 HT solution is more than an order of magnitude larger than that in the pristine P3 HT solution, as seen in Figure 3d, which is attributed to enhanced \(\pi\)-\(\pi\) stacking of the polymer chains by the aggregation of the P3 HT chains. The strong intermolecular interaction results in the formation of the ordered region with larger crystallites. The crystallite size in the sonicated P3 HT film is, indeed, calculated to be 13 nm from the Debye-Scherrer method, while, for the pristine P3 HT, the presence of the ordered region is not ensured from the GIXD data in Figure 1a. In other words, far higher drain current in the sonicated P3 HT in comparison with that in the pristine P3 HT clarifies that preferred P3 HT chain alignment in the sonicated P3 HT, resulting in enhanced molecular ordering, dominates over the formation of current path in determining the drain current. Indeed, from the optical absorption data in Figure 4a,b, anisotropic orientation is more prominent in the sonicated P3 HT. Two peaks at 570 and 610 nm in Figure 4a are identified with 0-1 and 0-0 vibrational peaks, respectively. The presence of the two peaks in the sonicated P3 HT solution explains more prominent \(\pi\)-\(\pi\) stacking-induced aggregation due to enhanced P3 HT interchain interactions [16]. After solidification, the ultrasonic irradiation process increases the planarity of the conjugated P3 HT chains, developing fine structure at \(\sim\)610 nm arising from interchain absorption. The magnitude of the absorbance is commensurate with the degree of molecular ordering [9]. In other words, a comparison of optical absorption between the solution and film states in Figure 4 clarifies that the anisotropic  
Figure 3: (**a**) A schematic diagram of the test structure for investigating the temporal evolution of the source (S)-drain (D) current. The ceramic tube confines a drop of P3 HT solution (5 mg/mL) into the channel region during solidification. The inset shows an image of the experimental set-up. The channel length and the width of the device were 20 \(\upmu\)m and 8 mm, respectively. Temporal evolution of the source-drain current in (**b**) pristine and (**c**) sonicated P3 HT solution. The concentration of the P3 HT solution in chloroform was 5 mg/mL. The drain voltage was fixed at 0.3 V, and the measurement was carried out in an argon-filled glove box. (**d**) Comparison of temporal change in the drain current (logarithmic scale). nature of the polymer chains in solution state was retained after solidification, which is in accordance with a far higher current in the sonicated P3 HT, as shown in Figure 3d. More importantly, for the sonicated P3 HT in Figure 3c, we reproducibly observed a significant current decrease after the current peak at 12 min following a dramatic increase in the current, while, for the pristine P3 HT in Figure 3b, a less sharp current peak at 6 min is observed as the solvent evaporates with time. In our previous study, we found that the change in the source-drain current depends on the solvent-P3 HT chain interactions as well as the boiling point of the solvent [10]. We hypothesize that the more anisotropic nature of the P3 HT molecules in the sonicated P3 HT solution, as demonstrated in the optical absorption feature in Figure 4, leads to a more significant decrease in the current after the peak current. The presence of the significant current peak results from a competition between vibration-induced aggregation of the disentangled P3 HT chains (increasing the current) and immobilization of the chains during solidification, through which the concentration of P3 HT solution is increased (decreasing the current).