Abstract
We develop a generic coarse-grained model of soluble conjugated polymers, capable of describing their self-assembly into a lamellar mesophase. Polymer chains are described by a hindered-rotation model, where interaction centers represent entire repeat units, including side chains. We introduce soft anisotropic nonbonded interactions to mimic the potential of mean force between atomistic repeat units. The functional form of this potential reflects the symmetry of the molecular order in a lamellar mesophase. The model can generate both nematic and lamellar (sanidic smectic) molecular arrangements. We parametrize this model for a soluble conjugated polymer poly(3-hexylthiophene) (P3HT) and demonstrate that the simulated lamellar mesophase matches morphologies of low molecular weight P3HT, experimentally observed at elevated temperatures. A qualitative charge-transport model allows us to link local chain conformations and mesoscale order to charge transport. In particular, it shows how coarsening of lamellar domains and chain extension increase the charge carrier mobility. By modeling large systems and long chains, we can capture transport between lamellar layers, which is due to rare, but thermodynamically allowed, backbone bridges between neighboring layers.
Highlights
Soluble semiconducting polymers are promising materials for manufacturing flexible, lightweight electronic devices using scalable and low-cost technologies, such as printing.[1−4] Polymer solubility and processability are achieved by mitigating the attraction of conjugated backbones with flexible alkyl side chains
We develop a generic coarse-grained model of soluble conjugated polymers, capable of describing their selfassembly into a lamellar mesophase
We have developed a generic coarse-grained model that can be used to simulate amorphous, nematic, and partially ordered lamellar mesophases of polymeric semiconductors
Summary
Soluble semiconducting polymers are promising materials for manufacturing flexible, lightweight electronic devices using scalable and low-cost technologies, such as printing.[1−4] Polymer solubility and processability are achieved by mitigating the attraction of conjugated backbones with flexible alkyl side chains. This approach, retains the hard excluded volume.[31,32] In soft models, a more general route is to construct the anisotropic potentials using the symmetry of the molecular order in different mesophases.[33] Using this approach, we devise a generic soft model that can simulate amorphous, nematic, and partially ordered lamellar mesophases, even though cyclic moieties and side chains are not explicitly resolved We use this model to study self-assembly and charge transport in poly(3-hexylthiophene) (P3HT). These mesophases are compared with experimentally reported structures of partially ordered lamellae (phase III),[42] which belong to the general class of sanidic liquid-crystalline mesophases.[44,45] They can be used to drive soluble polymeric semiconductors into solid-state morphologies with improved electronic properties.[5,45,46] Subsequently, we simulate largescale morphologies with different degrees of lamellar order and heterogeneity and use a qualitative charge-transport model[37−39] to link charge mobility to mesoscopic molecular organization
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