Organic Semiconductors: Impact of Disorder at Different Timescales

Abstract

The charge transport in organic materials, from molecular crystals to polymers, is determined by their degree of disorder. The dynamic disorder in ideal molecular crystals at room temperature and the static disorder in disordered polymers are just two limiting cases of the timescale of the fluctuations in the electronic Hamiltonian caused by nuclear motions. In fact, a very large number of important materials (e.g. liquid crystalline semiconductors) are actually in an intermediate regime where the disorder is neither purely static nor purely dynamic. This Minireview discusses the recent contribution of computational chemistry (molecular dynamics and quantum chemistry) to the characterization of these transport regimes and outlines the theoretical methods that can be used to relate the system characteristics to the measurable mobility.

Effect of dynamic disorder on charge transport along a pentacene chain

“…As stated above, this work is not intended to relate the disorder in the on-site energies to temperature or other sources of fluctuations that might occur in the system. It is highly unlikely, however, that such fluctuations will be larger than those in the transfer integral 23,26 since, as pointed out above, both these types of fluctuations result from intermolecular interactions. Consequently, the major effect of dynamical disorder in molecular crystals comes from fluctuation in the transfer integral in the way described in Fig.…”

Theoretical study of stability and charge-transport properties of coronene molecule and some of its halogenated derivatives: A path to ambipolar organic-based materials?

“…Also note that G is the energy difference (driving force) between initial and final states, which vanishes for equivalent molecules (self-exchange reaction). Nuclear tunnelling effects, as well as disorder effects caused by vibrational fluctuations of molecules at room temperature, 35,36 will not be considered; the effective incorporation of these effects would need the consideration of more complex physical models [37][38][39][40] which are however beyond the scope of this study.…”

Microscopic Simulations of Charge Transport in Disordered Organic Semiconductors

“…This can be achieved using semiclassical dynamics based on a Hamiltonian with interacting electronic and nuclear degrees of freedom. 23−25 If nuclear dynamics are much slower than the dynamics of charge carriers and electronic coupling is weak, charge transport can be described by a Hamiltonian with static disorder, based on simple assumptions on the electronic density of states and on the hopping rates between localized states.…”