Organic light emitting diodes (OLEDs), organic solar cells, organic thin films transistors, etc. are made of organic polymers or crystals
]. The effect of the disorder in organic devices on optoelectronic properties was analyzed by Rim et al.
]. They showed an increased photocurrent generation with improved molecular order. It occurs due to the influence of the stacking on the exciton diffusion length. Hu et al. measured a strong dependence of the conductance across highly oriented pentacene nanocrystals on the packing orientation
]. The influence of packing on charge transport in organic solids was also analyzed using Monte Carlo methods
]. Kwiatkowski et al.
] were able to predict the mobilities of electron and holes for ordered and disordered Alq3. Different functional organic materials were reviewed by Ishii et al.
]. They highlighted the energy level alignment and electronic structures at organic/inorganic and organic/organic interfaces of, for example, Alq3, 3,4:9,10-perylenetetracarboxylic dianhydride (PTCDA) and 1,4,5,8-tetrathiafulvalene (TTF).
In our work, the morphology of interfaces between pentacene
] and PTCDA
] was analyzed (Figure
a). Both molecules form different crystal modifications. Pentacene is known to have a high temperature (HT) and a low temperature (LT) polymorph. Yoneya et al.
] showed that the LT polymorph is destabilized by substrates and transforms into HT polymorph. Therefore, the HT polymorph was used as the base for simulations. For PTCDA, the α
] was used.
Figure 1 Pentacene and PTCDA: Chemical formulas and interface formation. (a) Chemical formulas of PTCDA (top) and pentacene (bottom) are presented. (b) Example of the realistic interface formed by PTCDA (212) on pentacene (100). After full MD relaxation cycle, (more ...)
Molecular orientation at interfaces is decisive for predicting optoelectronic properties such as exciton diffusion length
], charge carrier mobility
], and molecular quadrupole moments
]. Verlaak et al. analyzed the impact of the molecular quadrupole moments, influenced by e. g., material and crystal orientation on the interface energetics. An insight on models of electronic processes across organic interfaces is given by Beljonne et al.
], while a review of the corresponding theoretical approaches is presented by Brédas
Our study of organic-organic pentacene/PDCDA interfaces is organized as follows: after a brief introduction presented above, we proceed with the presentation of the methods followed by the results and some conclusive remarks.