Optical and Transport Anisotropy in Poly(9,9$'$-dioctyl-fluorene-alt-bithiophene) Films Prepared by Floating Film Transfer Method
We demonstrated the fabrication of self-aligned poly(9,9$'$-dioctyl-fluorene- alt -bithiophene) copolymer (F8T2) thin films at ambient temperature with a new solution-process technique named floating film transfer method (FTM). Atomic force microscope topography and polarized absorption spectro...
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| Published in | Japanese Journal of Applied Physics Vol. 51; no. 5; pp. 055802 - 055802-6 |
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| Main Authors | , , , |
| Format | Journal Article |
| Language | English |
| Published |
The Japan Society of Applied Physics
01.05.2012
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| Online Access | Get full text |
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| Summary: | We demonstrated the fabrication of self-aligned poly(9,9$'$-dioctyl-fluorene- alt -bithiophene) copolymer (F8T2) thin films at ambient temperature with a new solution-process technique named floating film transfer method (FTM). Atomic force microscope topography and polarized absorption spectroscopy showed that the polymer main chains aligned perpendicularly to the film propagation direction during the fabrication process. FTM films presented absorption dichroic ratios slightly below 3. Top-contact/bottom-gate field effect transistors made with FTM films exhibited anisotropic transport properties with a hole mobility along the aligned direction of F8T2 main chains of $2.2\times 10^{-3}$ cm 2 /(V$\cdot$s), which was around 2.5 times greater than that along the perpendicular direction. Dichroic and transport anisotropy ratios were further enhanced up to 7--8 by thermal annealing, although the mobility improvement remained limited due to possible trapping effect at domain boundaries. |
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| Bibliography: | (a) Picture of a F8T2 branched floating film when the solution is dropped at the center of a Petri Dish. (b) Orientation is clearly observed when observing through a linear polarizer. (c) Orientation is switched by rotating the polarizer 90°. The arrows in (b) and (c) indicate the transmission axis of the polarizer. Polarized absorption spectra of a FTM film before and after annealing ($\parallel$: prism parallel to the main chain orientation, $\perp$: prism perpendicular to the main chain orientation). Chemical structure of F8T2 is also presented in inset. (a) AFM image of an as-cast spin coated film ($5\times 5$ μm 2 ). (b) AFM image of an as-cast FTM film ($5\times 5$ μm 2 ) with a magnified image in the inset ($2\times 2$ μm 2 ). Schematic representation of the channel orientation for oriented FTM thin films OFETs. Typical transfer characteristics of OFETs made with as-cast F8T2 thin films (a) and annealed thin films (b). |
| ISSN: | 0021-4922 1347-4065 |
| DOI: | 10.1143/JJAP.51.055802 |