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Octadecyltriethoxysilane is very bulky (source),
yet it was used to promote single crystal growth (source). How can such a bulky molecule induce crystal growth? (For example epitaxial growth happens only when both materials have similar unit cell dimensions.)
The function of the octadecyltriethoxysilane monolayer in this case is not to promote epitaxial growth but to reduce the surface energy of the dielectric layer (SiO2), on top of which the semiconductor (pentacene/rubrene/etc.) is about to be deposited. The reduced surface energy allows the crystal to grow "comfortably".
Organosilanes are typical compounds for modifying oxide layers (Pernstich et al., 2004):
