Mixing-induced anisotropic correlations in molecular crystalline systems

TL;DR

This study reveals unique anisotropic disordering in mixed organic semiconductor films, showing in-plane disorder with preserved out-of-plane order, and introduces a mean field model to explain these phenomena.

Contribution

It reports a novel disordering behavior in mixed organic semiconductor films and proposes an anisotropic interaction model to explain the structural properties.

Findings

Equimolar PEN:DIP mixtures show in-plane disorder with out-of-plane order.

The disordering behavior is unreported in binary organic semiconductor mixtures.

The mean field model with anisotropic interactions helps rationalize the structural observations.

Abstract

We investigate the structure of mixed thin films composed of pentacene (PEN) and diindenoperylene (DIP) using X-ray reflectivity and grazing incidence X-ray diffraction. For equimolar mixtures we observe vanishing in-plane order coexisting with an excellent out-of-plane order, a yet unreported disordering behavior in binary mixtures of organic semiconductors, which are crystalline in their pure form. One approach to rationalize our findings is to introduce an anisotropic interaction parameter in the framework of a mean field model. By comparing the structural properties with those of other mixed systems, we discuss the effects of sterical compatibility and chemical composition on the mixing behavior, which adds to the general understanding of interactions in molecular mixtures.