Effect of Structure and Disorder on the Charge Transport in Defined Self-Assembled Monolayers of Organic Semiconductors

Abstract

Self-assembled monolayer field-effect transistors (SAMFETs) are not only a promising type of organic electronic device but also allow detailed analyses of structure-property correlations. The influence of the morphology on the charge transport is particularly pronounced, due to the confined monolayer of 2D-π-stacked organic semiconductor molecules. The morphology, in turn, is governed by relatively weak van-der-Waals interactions and is thus prone to dynamic structural fluctuations. Accordingly, combining electronic and physical characterization and time-averaged X-ray analyses with the dynamic information available at atomic resolution from simulations allows us to characterize self-assembled monolayer (SAM) based devices in great detail. For this purpose, we have constructed transistors based on SAMs of two molecules that consist of the organic p-type semiconductor benzothieno[3,2-b][1]benzothiophene (BTBT), linked to a C or C alkylphosphonic acid. Both molecules form ordered SAMs; however, our experiments show that the size of the crystalline domains and the charge-transport properties vary considerably in the two systems. These findings were confirmed by molecular dynamics (MD) simulations and semiempirical molecular-orbital electronic-structure calculations, performed on snapshots from the MD simulations at different times, revealing, in atomistic detail, how the charge transport in organic semiconductors is influenced and limited by dynamic disorder.

Multifunctional and Tunable Surfaces Based on Pyrene Functionalized Nanoparticles

“…Adding aromatic dyes as additional functionality to the PA ligands (PA dye) is likely to impact not only the structural arrangement in the resulting SAMs but also their overall characteristics. A leading example, which led to the corroboration of such a structure property relationship, is the application of PA derivatives in SAM field effect transistors . To this end, subtle changes in the morphological SAM arrangement exert a profound impact onto the electrical properties.…”

Molecular Control of Internal Crystallization and Photocatalytic Function in Supramolecular Nanostructures

“…When working with chromophore assemblies that possess highly ordered crystalline domains, 16–20 it should also be possible to control the crystal packing through slight modifications to the supramolecular monomers, an effect which has already been documented for organic single crystals, 21–23 and self-assembled monolayers. 24 …”

Simulation of charge transport in organic semiconductors: A time-dependent multiscale method based on nonequilibrium Green's functions

“…In Refs. [15,16], we have investigated charge transport in such SAMs based on a simpler methodology, which uses Landauer transport theory [17] for selected structural snapshots along a molecular-dynamics trajectory and time-averaging to obtain the electrical current. As has been shown previously [7], such an approach may fail for systems with fast-fluctuating electronic parameters, where, in particular, a simple adiabatic separation between the electronic and the ionic motion, causing the time dependence of the parameters in the Hamiltonian, is not possible.…”