Three-Dimensional Molecular Packing of Thin Organic Films of PTCDI-C8 Determined by Surface X-ray Diffraction

We have determined the full molecular 3D packing of thin organic films of the archetypical organic n-type semiconductor N,N′-dioctyl-3,4:9,10-perylene tetracarboxylic diimide (PTCDI-C8) by surface X-ray crystallography. We show that PTCDI-C8 forms smooth layered films on Al2O3 (11−20) with an outstanding degree of molecular order. The thin-film structure is found to consist of a triclinic unit cell with the plane of the aromatic core tilted by 67 ± 2° with respect to the surface plane, which differs significantly from the bulk structure. The 3D crystallites extend with vertical coherent order across the entire film thickness.