Morphological and transistor studies of organic molecular semiconductors with anisotropic electrical characteristics

Oriented thin films of organic semiconducting small molecules were prepared by crystallization on rubbed alignment layers. Polarized absorption spectr a showed that the long axis of the conjugated backbones was highly oriented along the rubbing direction and parallel to the substrates. Transmission e lectron microscopy and diffraction confirmed that the molecules and in many cases the resulting crystals are aligned. Using the above aligned films as semiconducting layers, we fabricated field-effect transistors having aniso tropic mobilities with ratios greater than 15. Several common organic semic onductors have been investigated, and the results indicate that this growth method is generally successful for achieving macroscopic alignment of thes e semiconducting molecules (and frequently their crystals, as well).