  Blended organic thin films have been studied during the last decades due to
their applicability in organic solar cells. Although their optical and
electronic features have been examined intensively, there is still lack of
detailed knowledge about their growth processes and resulting morphologies,
which play a key role for the efficiency of optoelectronic devices such as
organic solar cells. In this study, pure and blended thin films of copper
phthalocyanine (CuPc) and the Buckminster fullerene (C60) were grown by vacuum
deposition onto a native silicon oxide substrate at two different substrate
temperatures, 310 K and 400 K. The evolution of roughness was followed by
in-situ real-time X-ray reflectivity. Crystal orientation, island densities and
morphology were examined after the growth by X-ray diffraction experiments and
microscopy techniques. The formation of a smooth wetting layer followed by
rapid roughening was found in pure CuPc thin films, whereas C60 shows a fast
formation of distinct islands at a very early stage of growth. The growth of
needle-like CuPc crystals loosing their alignment with the substrate was
identified in co-deposited thin films. Furthermore, the data demonstrates that
structural features become larger and more pronounced and that the island
density decreases by a factor of four when going from 310 K to 400 K. Finally,
the key parameters roughness and island density were well reproduced on a
smaller scale by kinetic Monte-Carlo simulations of a generic, binary lattice
model with simple nearest-neighbor interaction energies.
