A n-vector model for charge transport in molecular semiconductors

Abstract

We develop a lattice model utilizing coarse-grained molecular sites to study charge transport in molecular semiconducting materials. The model bridges atomistic descriptions and structureless lattice models by mapping molecular structure onto sets of spatial vectors isomorphic with spin vectors in a classical n-vector Heisenberg model. Specifically, this model incorporates molecular topology-dependent orientational and intermolecular coupling preferences, including the direct inclusion of spatially correlated transfer integrals and site energy disorder. This model contains the essential physics required to explicitly simulate the interplay of molecular topology and correlated structural disorder, and their effect on charge transport. As a demonstration of its utility, we apply this model to analyze the effects of long-range orientational correlations, molecular topology, and intermolecular interaction strength on charge motion in bulk molecular semiconductors.

Influence of Vapor Deposition on Structural and Charge Transport Properties of Ethylbenzene Films

“…42 Regarding the decrease in the site-energy disorder, this effect is in agreement with the observed trends in the structural ordering of the films. Since the site energy of the hole state of a molecule depends strongly on the relative orientation of the neighboring dipoles, 35 the increased structural ordering of the film should lead, on average, to a more uniform dipolar environment around each ethylbenzene molecule, 43 leading to decreased energetic disorder.…”

“…Regarding the decrease in the site-energy disorder, this effect is in agreement with the observed trends in the structural ordering of the films. Since the site energy of the hole state of a molecule depends strongly on the relative orientation of the neighboring dipoles, the increased structural ordering of the film should lead, on average, to a more uniform dipolar environment around each ethylbenzene molecule, leading to decreased energetic disorder.…”

Role of intermolecular charge delocalization and its dimensionality in efficient band-like electron transport in crystalline 2,5-difluoro-7,7,8,8-tetracyanoquinodimethane (F2-TCNQ)

“…3,11 In the case of (quasi)1D transport along the stacks, a single defect in the stack can damage the transport pathway, while in the case of 3D transport, charges can easily circumvent the obstacle. [30][31][32] Summing up, the dimensionality of intermolecular charge delocalization explains the outstanding band-like electron transport in the F 2 -TCNQ crystal and inefficient hopping transport in TCNQ, which was the second issue addressed in the study.…”

Improved Scaling of Molecular Network Calculations: The Emergence of Molecular Domains

“…At larger system sizes we had originally expected the that R NET would either slightly increase or remain constant due to the minimization of the “surface effect”, where network fragmentation often starts at the surface of the molecular aggregate. The unexpected decrease in R NET for PDI points to the importance of larger system sizes, where larger scale morphologies like domain boundaries can come into play, and their effect on charge transport is not negligible …”

“…In the past, we have used coarse-grained charge-hopping models and Monte Carlo lattice models. While these models are qualitatively descriptive, to move to quantitative descriptions there needs to be a scale-up in the capacity of molecular orbital sparse data structures . Integration of sparse data operations into quantum-chemistry solvers is key to achieve the scale in orbital construction on the mesoscale.…”