We study the growth of two n-type small-molecule organic semiconductors from the perylene diimide family: N,N′-bis-(2-ethylhexyl)dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDIR-CN 2 ) and N,N′-1H,1Hperfluorobutyl-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDIF-CN 2 ) whose chemical structures differ only in the imide substituents, branched alkyl chains −C 8 H 16 and linear fluoroalkyl chains −C 4 F 7 H 2 , respectively. Both types of substituents introduce some degree of steric hindrance for intermolecular interactions, affecting solid-state packing during thin film formation, and thus induce specific structure-dependent optoelectronic properties in thin films. The transition from an amorphous structure to crystalline domains with strong intermolecular coupling was followed in situ and in real time during growth. We investigated the structural and morphological properties by X-ray diffraction and atomic force microscopy as a function of the substrate temperature and chemical structure. We examined the relationship between the structural properties and thin film optical signatures probed via differential reflectance spectroscopy, ellipsometry, and temperature-dependent photoluminescence. A new crystalline PDIR-CN 2 polymorph at high temperatures emerges. In addition, we observed in PDIF-CN 2 that the fluorinated chains contribute to crystallization inhibition because of the higher overall steric hindrance compared to the alkyl chains.

In organic electronics and optoelectronics several crucial physical processes are related to charge transfer (CT) effects. In this work, we investigate mixing behavior and intermolecular coupling of donor and acceptor molecules in thin films prepared by organic molecular beam deposition (OMBD). Diindenoperylene (DIP) and pentacene (PEN) are used as the donor materials, and perylene diimide derivatives PDIR-CN 2 and PDIF-CN 2 as the acceptor materials.. The formation of charge transfer complexes coupled in the electronic excited state vs. noninteracting phase separating components is studied by structural and optical techniques. The CT mechanism and properties are considered in close connection with the thin film microstructure of the D/A blends which can be controlled via a change of the molecule geometry and/or growth temperature. We discuss two key findings for our systems: (1) The CT intensity correlates directly with the possibility of cocrystallization between acceptor and donor. (2) Side chain modification to tune the ground state energy levels has nearly no effect on the energy of the excited state CT, whereas replacement of molecular core modifies the CT energy correspondingly.

Deposition on patterned substrates is a promising method for obtaining high quality, strain and defect free heteroepitaxial layers. In this paper we investigate the crystalline structure of quasi-continuous Ge layers consisting of closely spaced microcrystals on a Si substrate patterned in the form of a regular net of lithographically defined squared based pillars. Lattice parameters, strain and degree of relaxation of the Ge microcrystals are measured by standard high-resolution X-ray diffraction using reciprocal space mapping. In particular, we focus on the impact of Si pillar size and spacing on the Ge crystal quality by analyzing how the bending of crystal lattice planes caused by thermal stress relaxation and random crystal tilts affect the width of the diffraction peaks.