Aligned rrP3HT film: Structural order and transport properties

Aligned regioregular poly(3 hexyl thiophene), rrP3HT, thin films have been fabricated by a rubbing technique. Structural studies indicate orthorhombic crystalline domains (CDs) with c-axis aligned principally along the rubbing direction. The backbones of the macromolecules are stacked along the b-axis, forming a plane of parallel backbones with π-electron overlap and with side chains between the planes (along the a-axis). There is no π-overlap between these planes due to the long side chains along the a-axis. The optical and electronic properties are correlated with the anisotropic structure. Both for light polarized parallel and for light polarized perpendicular to the chain direction, the onset of photocurrent coincides with the onset of absorption. The larger photoconductivity observed with light polarized along the c-axis suggests the films are of sufficiently high quality to reveal the intrinsic anisotropy of the electronic structure.