Optical and Transport Anisotropy in Poly(9,9\u27-dioctyl-fluorene-alt-bithiophene) Films Prepared by Floating Film Transfer Method

We demonstrated the fabrication of self-aligned poly(9,9\u27-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 2.2×10-3 cm2/(Vcenterdots), 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