Bi-axially aligned crystallites of a fluorene-bithiophene co-polymer

Thin films of the soluble conjugated poly(9,9-dioctylfluorenyl-co-bithiophene) (F8T2) on top of polyimide surfaces were investigated by X-ray diffraction measurements, atomic force and optical microscopy. In-situ temperature dependent specular X-ray diffraction experiments reveal the formation crystallites on heating. An orthorhombic unit cell of a = 1.61 nm, b = 1.28 nm and c = 6.2 nm was found which results in 16 monomer units being hosted in the unit cell at a density of 1.15 g cm3. Morphology investigations reveal random azimutal orientations of spherulite like structures are present for samples prepared on the isotropic surface. Using a defined preparation route allowed for the alignment of the crystallites with respect of a rubbed polyimide surface resulting in bi-axially aligned F8T2 crystals as determined by X-ray diffraction polefigure measurements and optical microscopy.