Simulating Self-Assembly of Organic Molecules & Classifying Intermolecular Dispersion

Abstract

Mechanisms for charge transport in organic electronics allows them to perform with disordered internal morphology, something which is not possible for traditional crystalline semiconductors. Improvements to performance can occur when the materials change their relative positions to each other, resulting as a different spatial dispersion with lower electrical loss over the device area.

A numerical method has been developed using interaction models for molecules from colloidal self-assembly. Colloids are rigid particles with a volume which is embodied by their shape and their collective behaviour depends on its density. The self-assembly mechanism used is condensation, which increases the density by removing the spaces between molecules while they lose thermal energy due to the increasing steric interactions with neighbours. The molecular chemical structure determines the spatial probability of electron orbitals that (for a given energy) outlines their geometric shape. Because these shapes are localized onto the molecule, their intermolecular positions determine how close these orbitals can be to each other which is important for electron charge transport.

During operation, the organic active layer may have thermal energy to cause molecular reorganization before cooling, which increases the probability to find disordered states within the device. A comprehensive suite of tools has been developed which can classify disorder in the physical characteristics of morphology; such as density, internal spacing, and angular orientation symmetry. These tools where used to optimize the experimental preparations for depositing nanoparticle dispersions on surfaces within organic electronic devices. These have also been used to quantify the statistical variations in structure between configurations produced from our Monte Carlo method and a similar molecular dynamics approach. Simulated self-assembly within highly confined areas showed repeatedly sampled microstates, suggesting that at thermodynamic equilibrium confined particles have quantized density states. We conclude with morphologies resulting from non-circular shapes and systems of donor-acceptor type molecules.