Charge-Transport Anisotropy Due to Grain Boundaries in Directionally Crystallized Thin Films of Regioregular Poly(3-hexylthiophene)

The problem of transport across grain boundaries in semicrystalline polymers was investigated quantitatively using a directional crystallization technique to make anisotropic thin films of poly(3-hexylthiophene) (P3HT) with controlled grain-boundary placement and orientation. 1,3,5-trichlorobenzene (TCB), a small-molecule solvent that is solid at room temperature, acts first as a solvent and second as a substrate for polymer epitaxy. The solvent/polymer solution is then undercooled, allowing for the selective crystallization of TCB to be induced by the introduction of a heat sink. Atomic force microscopy (AFM) confirms the presence of a continuous film, and reveals the anisotropic fiber structure. The X-ray scattering data confirms the semicrystalline nature of the films, and reveals a pronounced in-plane film texture. The high-resolution GIXS experiments confirm the crystalline anisotropy in the plane of the substrate.