Methods and materials for preparing organic semiconducting layers include, for example, one used in an organic semiconductor device including a substrate with a nano structured surface and an organic semiconductor film overlying the nanostructured surface. The semiconductor film is typically formed from macroscopically ordered polymer fibers made from selected conjugate polymer compounds. Such polymer fibers synthesized from selected conjugated polymer compounds and directionally aligned in organic semiconductor devices can provide these devices improved functional properties, including for example, unexpectedly high field effect saturation mobilities.