The intramolecular and intermolecular charge transport parameters are evaluated quantum chemically for three fluorinated derivatives of perylene bisimide (PBI) semiconductors, two of which feature a twisted PBI core. Charge transfer rates are computed within the Marcus-Levich-Jortner formalism including a single effective mode treated quantum mechanically and are injected in a kinetic Monte Carlo scheme to propagate the charge carrier in the crystal and to estimate charge mobilities at room temperature. The relative order of computed mobilities agrees with the observed trend, and the largest mobility is computed for the planar PBI derivative. It is suggested that thermally induced disorder effects should contribute considerably to the observed large mobility of the planar PBI derivative, while a retardation effect induced by the presence of alternating slow and fast jumps along pi-stacked PBI columns is responsible for the lower mobilities of the two twisted derivatives. The computed parameters reveal the subtle interplay between intramolecular and intermolecular contributions to the charge carrier propagation in these organic semiconductors and may guide the design of more efficient architectures.

We built a model of charge transport in a single disordered polymer chain starting from a model Hamiltonian of the system. The parameters entering the Hamiltonian determine both the density of states (DOS) and the hopping rate unlike the most common modelling strategies of transport in polymeric materials that parametrize both the DOS and the hopping rate from the outset. This model incorporates the effect of variable delocalization of one-electron states and is designed to link atomistic calculations of polymeric systems with full device models in multiscale modelling protocols. The initial and final states for the hopping process are determined by static disorder and further stabilized by polaronic effects. The coupling between these states is due to the residual (and much smaller) dynamic disorder. We find that, at lower static disorder, long-distance hopping events become more frequent, i.e. the hopping range and disorder are not unrelated parameters, as commonly assumed. The availability of low energy relatively delocalized states promotes long range displacement of charge and it can be at the origin of the high mobility observed in some polymers. The description of the hopping rates from the model Hamiltonian also allows the identification of the breakdown of the incoherent transport limit.

In this paper, the exciton transport properties of an octa(butyl)-substituted metal-free phthalocyanine (H2-OBPc) molecular crystal have been explored by means of a combined computational (molecular dynamics and electronic structure calculations) and theoretical (model Hamiltonian) approximation. The excitonic couplings in phthalocyanines, where multiple quasi-degenerate excited states are present in the isolated chromophore, are computed with a multistate diabatization scheme which is able to capture both short-and long-range excitonic coupling effects. Thermal motions in phthalocyanine molecular crystals at room temperature cause substantial fluctuation of the excitonic couplings between neighboring molecules (dynamic disorder). The average values of the excitonic couplings are found to be not much smaller than the reorganization energy for the excitation energy transfer and the commonly assumed incoherent regime for this class of materials cannot be invoked. A simple but realistic model Hamiltonian is proposed to study the exciton dynamics in phthalocyanine molecular crystals or aggregates beyond the incoherent regime.2

The narrower bands formed by donor–acceptor polymers are not detrimental to transport, as the reduced electronic coupling along the chain is more than compensated by a reduced activation energy for transport. These polymers are less sensitive to the conformational disorder of the chain as long as the bandwidth is larger than a threshold.

We describe charge transport along a polymer chain with a generic theoretical model depending in principle on tens of parameters, reflecting the chemistry of the material. The charge carrier states are obtained from a model Hamiltonian that incorporates different types of disorder and electronic structure (e.g. the difference between homoand co-polymer). The hopping rate between these states is described with a general rate expression, which contains the rates most used in the literature as special cases. We demonstrate that the steady state charge mobility in the limit of low charge density and low field ultimately depends on only two parameters: an effective structural disorder and an effective electron-phonon coupling, weighted by the size of the monomer. The results support the experimental observation [N. I. Craciun, J. Wildeman, and P. W. M. Blom, Phys. Rev. Lett. 2008, 100, 056601] that the mobility in a broad range of (polymeric) semiconductors follows a universal behaviour, insensitive to the chemical detail.

Symmetric aqueous organic redox flow batteries (RFBs) are potentially an inexpensive, durable, and safe energy storage technology. Unlike normal asymmetric flow batteries, they are based on electrolytes that exist in at least three oxidation states and can undergo a minimum of two distinct redox processes. We compute the redox potentials of selected electrolytes, with the intent to understand how the interaction between the redox units affects the potentials. We find that electronic interaction between redox units and intramolecular hydrogen bonding can be exploited to tune the difference between the redox potentials, i.e., the theoretical voltage of the battery. The redox potentials can be further fine-tuned in either direction by adding substituents. Starting from these observations, we formulate a set of rules that will help in finding ideal candidates for symmetric RFBs.

Organic redox‐active battery materials are an emerging alternative to their inorganic counterparts currently used in the commercialized battery technologies. The main advantages of organic batteries are the potential for low‐cost manufacturing, tunability of electrochemical properties through molecular engineering, and their environmental sustainability. The search for organic electroactive materials that could be used for energy storage in mobile and stationary applications is an active area of research. Computer simulations are used extensively to improve the understanding of the fundamental processes in the existing materials and to accelerate the discovery of new materials with improved performance. We will focus on two main types of redox‐active organic battery materials, that is, solid‐state organic electrode materials and organic electrolytes for redox flow batteries. Because organic materials are made of molecular building blocks, the molecular modeling methodology is usually the most appropriate to investigate their properties at the electronic and atomistic scales. After introducing the fundamentals of computational organic electrochemistry, we will survey its most recent applications in organic battery research and outline some of the remaining challenges for the development and applications of atomic‐scale modeling techniques in the organic battery context. This article is categorized under: Structure and Mechanism > Computational Materials Science Software > Molecular Modeling Electronic Structure Theory > Density Functional Theory

We propose an expression of the hopping rate between localized states in semiconducting disordered polymers that contains the most used rates in the literature as special cases. We stress that these rates cannot be obtained directly from electron transfer rate theories as it is not possible to define diabatic localized states if the localization is caused by disorder, as in most polymers, rather than nuclear polarization effects. After defining the separate classes of accepting and inducing nuclear modes in the system, we obtain a general expression of the hopping rate. We show that, under the appropriate limits, this expression reduces to (i) single-phonon rate expression or (ii) the Miller-Abrahams rate or (iii) a multi-phonon expression. The description of these limits from a more general expression is useful to interpolate between them, to validate the assumptions of each limiting case, and to define the simplest rate expression that still captures the main features of the charge transport. When the rate expression is fed with a range of realistic parameters the deviation from the Miller-Abrahams rate is large or extremely large, especially for hopping toward lower energy states, due to the energy gap law.