Effect of Solvent Vapor Annealing on Crystalline Structure and Carrier Mobility of Poly(3-hexylthiophene) Nanofibers

Regioregular poly(3-hexylthiophene) (rr-P3HT) nanofibers offer a combination of simple, low-cost fabrication and inherently high crystallinity, making them promising materials for use as conductive polymer semiconductors in organic electronics. This study clarified how solvent vapor annealing (SVA) using chloroform as the solvent improves the internal structure of poly(3-hexylthiophene) (P3HT) nanofibers and consequently enhances their electrical performance. Nanofibers were fabricated from an anisole/chloroform mixture (3:7 v/v) and subsequently exposed to chloroform vapor for 6–12 h (powder samples) or 15–60 min (thin film mats). X-ray diffraction (XRD) analysis retained the native (100) and (020) reflections while also revealing higher-order (200), (300), and (400) peaks, along with a new (020)* peak associated with an enhanced crystallographic packing density along the π–π stacking direction as a result of the SVA treatment. The crystalline coherence length along the π–π stacking direction increased substantially from 32 Å in the pristine state to 82 Å after 12 h of SVA treatment. Simultaneously, the broad amorphous peak between 15° and 28° decreased, indicating the partial conversion of disordered regions into well-ordered crystalline domains. Scanning electron microscopy and atomic force microscopy analyses confirmed that the nanofiber morphology remained intact under the optimized SVA conditions. A bottom-gate field-effect transistor fabricated from rr-P3HT nanofiber mats exhibited p-type charge transport characteristics. After 60 min of SVA, the linear-regime mobility had increased by a factor of 1.3, from 5.27 × 10-3 to 6.86 × 10-3 cm2 V-1 s-1, which was accompanied by a reduced threshold voltage. The carrier mobility enhancement scaled positively with the SVA duration and showed a strong correlation with the increase in the crystalline coherence length. These findings collectively demonstrate that optimized chloroform SVA is a highly effective post-treatment strategy for densifying π–π stacking and improvin g charge transport without compromising the nanofiber morphology.