Novel Crystalline-Crystalline Diblock Copolymers and Polymer blends of Poly(3-hexylthiophene) and Poly(Stearyl acrylate) for Field-Effect Transistors
Date Issued
2011
Date
2011
Author(s)
Lin, Jung-Chuan
Abstract
Conjugated diblock copolymers or polymer blends could form nanostructured morphologies for optoelectronic device applications. Regioregular poly(3-hexylthiophene) is one of the widely studied π-conjugated polymer. However, amorphorous coil were used most of the P3HT based diblock copolymers or polymer blends for preparing nanostructured films. In this thesis, new crystalline poly(3-hexylthiophene)/poly(stearyl acrylate) polymer blends and poly(3-hexylthiophene-b-steryl acrylate) rod-coil block copolymers were explore for field-effect transistor applications, as described below.
1. Morphology and Field-Effect Transistor Characteristics of Crystalline Poly(3-hexylthiophene) and Poly(stearyl acrylate) Blends with solvent-induced Process (chapter 2): The field-effect transistors based on double-crystalline poly(3-hexylthiophene) (P3HT)/poly(stearyl acrylate) (PSA) blends system with high performance and low percolation threshold were investigated. The morphologies can be manipulated by using various solvents. In a marginal solvent of dichloromethane, the P3HT nano crystallites wires were generated in solution, but not in a good solvent of chloroform. Solvent -induced phase segregation of crystalline P3HT/PSA polymer blends provides a facile way to construct P3HT nanowires. The films prepared from CH2Cl2 tended to form well-defined nanowires with an average diameter of 30 nm, attributed to the self assembly of the P3HT segments. With decreasing the contents of P3HT, the number of the nanowires decreased significantly. The devices based on P3HT/PSA blends films with 2 wt% P3HT showed performance hole mobility of 3.2 × 10-3 cm2V-1s-1 and an excellent on/off ratio of 105-106, comparable with the homo-P3HT(3.3 × 10-3 cm2V-1s-1). Furthermore, P3HT/PSA blends with 2 wt% P3HT exhibited an excellent air stability even though exposure in air for a week, indicating the insulating crystalline PSA component plays a critical role for the improved air stability.
2. New Crystalline-Crystalline Diblock Copolymers of Poly(3-hexylthiophene-b-steryl acrylate) for Field Effect Transistors (chapter 3): The synthesis, charge transport and morphology of crystalline-crystalline diblock copolymers, poly(3-hexylthiophene-block-stearyl acrylate) (P3HT-b-PSA), with various PSA lengths are reported in this study. The new copolymers, with PSA coil lengths of 26, 50 and 360 repeating units, were synthesized by atom transfer radical polymerization (ATRP). The field-effect mobilities of P3HT-b-PSA were measured on the untreated and phenyltrichlorosilane(PTS)-treated SiO2 substrates. On the untreated SiO2 surface, the mobilities of the copolymers decreased with the increased PSA contents, from 3.41×10-4 cm2V-1s-1 (P1) to 2.26×10-6 cm2V-1s-1 (P3). In the sharp contrast, on the PTS-treated substrates, the diblock copolymers with the larger PSA content exhibited a higher mobility, from 4.51×10-4 cm2V-1s-1 (P1) to 4.16×10-3 cm2V-1s-1 (P3). The copolymers containing 14 mol% P3HT showed a good mobility of 4×10-3 cm2V-1s-1 and a high on/off ratio of 7×106 on the PTS-treated substrate. This is due to the fact that the interaction between phenyl groups and aromatic semiconducting polymers facilitated the orientation and induced the formation of more P3HT nanowires. This study provides the importance of the self-assembly monolayer at the interface for charge transport and morphology of the crystalline-crystalline diblock copolymers.
Subjects
Field effect transistor
polymer blends
conjugated block copolymer
Poly(3-hexylthiophene)
Poly(Stearyl acrylate)
Type
thesis
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