Morphology and Application of Electrospun Poly(3-hexylthiophene) Nanofibers on Field-effect transistor
Date Issued
2010
Date
2010
Author(s)
Chen, Jung-Yao
Abstract
Semiconductor based polymer nanostructures have potential applications in flexible electronic or optoelectronics, such as nanowire or nanofiber. The fabrication, morphology control, and electronic properties of electrospun nanofiber remain significant challenge. In this thesis, we used two-fluid coaxial electrospinning technique to prepare P3HT/PMMA core/shell polymer nanofiber, followed by extraction of PMMA to obtain pure P3HT nanofiber. The morphology and electronic properties of the prepared nanofiber show the enhanced carrier mobility through the optimization of process parameters, as described below:
1. Effects of Shell Flow-Rate on the Morphology and Electrical Properties of Coaxial Electrospun Poly(3-hexylthiophene) Nanofibers For Field-Effect Transistor(chapter 2): The P3HT fiber diameters after removing the shell PMMA were 168, 131, 257 and 520 nm using the different shell flow rates of 0.5, 1.0, 1.5, and 2.0 ml/hr, respectively. All of the above ES fibers are smooth and uniform because the electrospun solvent chlorobenzene with a high boiling point leading to more stable cone-jet model during ES process. The morphology studies show that the π-π stacking, crystallinity and crystal size of P3HT were significantly enhanced at the shell flow rate was reduced, which led to large charge-carrier mobility. The highest charge-carrier mobility as the shell flow rate of 1.0 ml/hr could be up to 1.92*10^-1 cm2/Vs. The higher electrical force along fiber axis at low shell flow rate probably induced preferred orientation of P3HT polymer chains in nanofiber and promoted the already-aligned polymer chains folding to be the better crystallinity and larger crystal size after annealing treatment. A schematic representation on the relationship between chain packing and charge transport in ES P3HT nanofiber is also provided in this chapter.
2. Effects of Solvent and thermal treatment on the Morphology and Electrical Properties of Coaxial Electrospun Poly(3-hexylthiophene) (P3HT) Nanofibers For Field-Effect Transistor (chapter 3): In this study, three different core solvents, chloroform(CF), chlorobenzene(CB), and 1, 2, 4-trichlorobenzene(TCB), were employed to manipulate the morphologies and electrical properties of ES P3HT nanofibers. The results show that the core solution viscosity plays an important role to control the morphology and charge-carrier mobility. In the lower viscosity solutions using chloroform, polymer chains completely extend can be fully stretched by electrical force, resulting in higher ordered orientation and charge-carrier mobility of the P3HT nanofiber even though processing lower crystallinity and thinner crystal size. On the other hand, the high solution viscosity using TCB led to the significant P3HT aggregation in solution but poor orientation within the nanofiber, leading to low carrier mobility. The highest charge-carrier mobility of prepared ES P3HT nanofiber based FET using chloroform system could be up to 3.57*10^-1 cm2/Vs, which suggest the importance of ES process on preferred orientation of polymer chains within fibers. The morphology and electrical properties were also investigated by thermal treatment at different temperature Morphology studies using SEM and XRD demonstrate that the thermal treatment decreases in the fiber diameter, increased P3HT crystallinity and affected carrier mobility. However, as temperature was higher than 100 ℃, the geometrical confinement begin to be destroyed, resulting in poor orientation within nanofiber, thereby decreasing the measured field-effect mobility. Our observations show that both the orientation and crystallinity affect the mobility and 100 ℃ is an optimum temperature of thermal treatment to prepare ES P3HT nanofiber FET.
The present study addressed the importance of the process parameters on the morphology and OFET device characteristics of the ES P3HT nanofiber.
Subjects
electrospun poly(3-hexylthiophene) nanofibers
flow rate
solvent effect
different temperature
organic field-effect transistor
Type
thesis
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