Microscopic origins of charge transport in triphenylene systems

Abstract

We study the effects of molecular ordering on charge transport at the mesoscale level in a layer of ≈9000 hexa-octyl-thio-triphenylene discotic mesogens with dimensions of ≈20 × 20 × 60 nm 3. Ordered (columnar) and disordered isotropic morphologies are obtained from a combination of atomistic and coarse-grained moleculardynamics simulations. Electronic structure codes are used to find charge hopping rates at the microscopic level. Energetic disorder is included through the Thole model. Kinetic Monte Carlo simulations then predict charge mobilities. We reproduce the large increase in mobility in going from an isotropic to a columnar morphology. To understand how these mobilities depend on the morphology and hopping rates, we employ graph theory to analyze charge trajectories by representing the film as a charge-transport network. This approach allows us to identify spatial correlations of molecule pairs with high transfer rates. These pairs must be linked to ensure good transport characteristics or may otherwise act as traps. Our analysis is straightforward to implement and will be a useful tool in linking materials to device performance, for example, to investigate the influence of local inhomogeneities in the current density. Our mobility-field curves show an increasing mobility with field, as would be expected for an organic semiconductor.

Charge Mobility in Discotic Liquid Crystals

“…Among the most studied compounds in the field of DLC are triphenylene derivatives, not only from the experimental point of view but also considering modelling [ 181 , 182 ]. Thompson and coworkers proposed an innovative analysis that easily provides the connection between microscopic properties and performance, investigating the relationship between molecular order and charge transport at the mesoscale, by analyzing a volume of around 20 × 20 × 60 nm 3 containing more than 9000 molecules of the hexa-octyl-thio-triphenylene discotic mesogen [ 182 ]. Both ordered columnar and disordered morphologies were modelled via MD, charge mobility was calculated through MC methods and the rapid increase of mobility upon switching from disordered to ordered morphology was simulated.…”

“…Moreover, compound 29 shows the highest transfe and calculated charge mobilities for both holes and electrons and, therefore, it c sidered as a potential candidate to be used in optoelectronics applications. Among the most studied compounds in the field of DLC are triphenylene derivatives, not only from the experimental point of view but also considering modelling [181,182]. Thompson and coworkers proposed an innovative analysis that easily provides the connection between microscopic properties and performance, investigating the relationship between molecular order and charge transport at the mesoscale, by analyzing a volume of around 20 × 20 × 60 nm 3 containing more than 9000 molecules of the hexa-octyl-thiotriphenylene discotic mesogen [182].…”

From idealised to predictive models of liquid crystals

“…Our contribution has been and still is that of trying to obtain morphologies for organic functional materials, some of which liquid crystalline, e.g. phthalocyanines [98] or perylene derivatives [99] or triphenylenes [100] forming columnar molecular organisations which can be used as input for calculation of charge transport or, in the case of donor-acceptor (D-A) Figure 13. (Colour online) On the left some 'hard' solid surfaces we have studied: hydrogen terminated silicon [95] (a), silica in a cristobalite quartz morpholgy (b) silica glass (c) [96], fullerene [93] (d) and on the right some 'soft' surfaces: self assembled monolayer (SAM) on: an alkylsilane (OTS) on silica glass [97] (e), a fluoroalkysilane (FDTS) SAM [97](f), and two polymers: PMMA [94] (g) and polystyrene [94](h).…”

A Bidimensional Gay-Berne Calamitic Fluid: Structure and Phase Behavior in Bulk and Strongly Confined Systems

“…Several GB parameterizations have reproduced nematic and smectic phases [102][103][104]. More recently, a discotic parameterization has been used to explore nematic and columnar phases [105][106][107][108][109], providing insight on structural and dynamic measurements at the molecular level [110][111][112]. The recognition of specific design principles has stimulated the attainment of novel targets [27].…”