Abstract
Organic semi-conductors have unique electronic properties and are important systems both at the fundamental level and also for their applications in electronic devices. In this article we focus on the particular case of rubrene which has one of the best electronic transport properties for application purposes. We show that this system can be well simulated by simple tight-binding systems representing one-dimensional (1D) chains that are weakly coupled to their neighboring chains in the same plane. This makes in principle this rubrene system somehow intermediate between 1D and isotropic 2D models. We analyse in detail the dc-transport and terahertz conductivity in the 1D and in the anisotropic 2D models. The transient localisation scenario allows us to reproduce satisfactorily some basics results such as mobility anisotropy and orders of magnitude as well as ac-conductivity in the terahertz range. This model shows in particular that even a weak inter-chain coupling is able to improve notably the propagation along the chains. This suggest also that a strong inter-chain coupling is important to get organic semi-conductors with the best possible transport properties for applicative purposes.
Highlights
Our goal is to show for rubrene and, within the transient localisation scenario [9,10], how the structure and the inter-chain coupling can affect the electronic conduction
Because of the small overlap between orbitals of different molecules the electron band and the hole band have very small width smaller than an eV
We show below a simplified treatment of the effect of this dynamical disorder in the context of a relaxation time approximation (RTA)
Summary
In this paper we present a description of quantum diffusion within a scenario that is known as transient localisation scenario [8,9] This scenario gives so far one of the best description [10] of transport in a system like rubrene C42 H28 which is known to possess one of the highest mobility at room temperature among organic semi-conductors. The hopping matrix element of this Hamiltonian are time dependent because of the motion of the molecules This transient localization scenario is not expected to apply to systems with much lower mobilities for which polaronic effects can be important.
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