Manipulation on the morphology and electrical properties of aligned electrospun nanofibers of poly(3-hexylthiophene) for field-effect transistor applications

We prepared aligned poly(3-hexylthiophene) (P3HT) nanofibers for the application of organic field-effect transistor (OFET) by two-fluid coaxial electrospinning (ES) technique using P3HT as core and PMMA as shell, followed by extraction of PMMA. Effects of shell flow rate and thermal annealing temperature on the morphology and optoelectronic properties were explored. The experimental results showed that the prepared P3HT nanofibers were highly aligned and their diameters were smaller in the case of low shell flow rate. The OFET carrier mobility of aligned P3HT ES nanofibers using the low shell flow rate could be dramatically improved up to 3 orders of magnitude (1.92 × 10^-1 cm²/V•s with the on/off ratio of 4.45 × 10⁴) in comparison with those from the high shell flow rate. The results of wide-angle X-ray scattering (WAXS) and photophysical properties (optical absorption and polarized photoluminescence) suggested the enhancement of π-π stacking and crystallinity of P3HT in the nanofibers at a lower shell flow rate, due to the higher electrical force along nanofiber axis. Besides, as thermal annealing temperature was higher than 100 °C, the relaxation of P3HT orientation in the nanofibers led to a reduction of the measured field-effect mobility. The experimental results addressed the importance of the process parameters (i.e., the shell flow rate and thermal annealing temperature) on tuning the chain packing and orientation of P3HT in nanofibers and the resultant OFET characteristics.