Enhancement of Spontaneous Orientation Polarization in Organic Semiconductor Mixtures

TL;DR

This paper investigates how surface equilibration and intermolecular interactions enhance spontaneous orientation polarization in mixed organic semiconductor films, leading to higher molecular alignment compared to neat layers.

Contribution

It provides a detailed discussion on the influence of surface equilibration and other interactions on molecular orientation in mixed organic films.

Findings

Surface equilibration affects molecular orientation in mixed layers.

Intermolecular interactions contribute to SOP enhancement.

Mixed films show higher alignment than neat layers.

Abstract

The alignment of permanent dipole moments and the resulting spontaneous orientation polarization (SOP) is commonly observed in evaporated neat films of polar organic molecules and leads to a so-called giant surface potential. In case of mixed films, often enhanced molecular orientation is observed, i.e.\ a higher degree of alignment, in comparison to neat layers, if it is diluted into a suitable (non-polar) host. So far, different possible influences on molecular orientation have been discussed, the most prominent probably being the so-called surface equilibration model. In this contribution, we discuss how surface equilibration can influence orientation in mixed layers, and which other intermolecular interactions have to be considered to explain the observed enhancement of SOP in mixed layers.