Synergistic Effect of Solvent and Epitaxy on the Formation of Anisotropic Structures of P3HT and P3HT/PCBM Films.

Oriented organic semiconductor blends can confer desirable properties, such as enhanced charge transport properties and polarized light emission or absorption. A technique that is not only adapted to solution processing but also producing anisotropic conducting blend films is realized by epitaxial crystallization of blends on oriented polymer substrate. The epitaxial structure of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) on oriented polyethylene (PE) substrate is affected by the boiling point of the used solvent. The P3HT spin-coated from o-dichlorobenzene with a high boiling point on PE forms a "side-on" and "face-on" molecular chain orientation with c-axis parallel to the c-axis of PE. While the orientation of the side-on and face-on is poor when P3HT is spin-coated from chloroform with a low boiling point. The addition of PCBM does not affect the epitaxial crystallization behavior of P3HT. Moreover, the anisotropic structure of PCBM is also obtained on the PE substrate. The PE substrate efficiently increases the amount of the face-on structure and the ratio of the face-on to side-on is 7 times that on the PSS:PEDOT substrate. Anisotropic structures lead to anisotropic absorption and photoluminescence properties. The anisotropic optical properties are better for the sample spin-coated from o-dichlorobenzene with the dichroic ratio of 2. The technique of employing oriented PE film to regulate the formation of oriented conducting polymer combined with the analytical method provides guidance to the fabrication and characterization of anisotropic functional film.