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Charge transport in supramolecular assemblies: An atomistic description

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Charge transport plays a key role in defining the performance of organic-based devices such as light-emitting diodes, solar cells, or field-effect transistors. Transport is typically described in two extreme cases, namely the band regime versus the hopping regime. I will argue in the first part of the talk that many electronic effects in organic semiconductors tend to favor a hopping picture in devices at room temperature. In this context, macroscopic models have been developed over the years to characterize the influence of several parameters (such as temperature, electric field amplitude, disorder, charge carrier density) on the mobility values. Most of them have in common to involve effective parameters that do not take fully into account the nature and relative position of the interacting molecules. On the other hand, quantum-chemical calculations have been extensively used recently to calculate all parameters governing the rate of charge transfer between two interacting molecules in the hopping regime; such an approach explicitly takes into account the chemical structure and actual packing of the molecules. I will survey some of our recent studies aiming at the description of the various transport parameters in a large variety of systems. I will also show that a bridge can be established between the molecular and macroscopic worlds by performing Monte-Carlo (MC) simulations based on the calculated transfer rates to be in position to evaluate charge mobility within the hopping regime in supramolecular assemblies from calculated molecular parameters; recent applications of this approach will be shown, for instance to characterize the anisotropy of charge transport in molecular crystals or the electric-field dependence of the mobility. Such simulations are typically performed nowadays on frozen structures, thus neglecting the impact of lattice dynamics. In the last part of the talk, I will show very recent results examining the way intermolecular vibrations modulate the key transport parameters and I will discuss the implications for charge transport properties.

This talk is part of the Optoelectronics Group series.

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