Representing the Molecular Signatures of Disordered Molecular Semiconductors in Size-Extendable Models of Exciton Dynamics.

This manuscript presents an approach to developing size-extendable phenomenological site-based models for simulating exciton dynamics in disordered organic molecular semiconducting materials. This approach extends an existing methodology that assigns the parameters of the time-dependent Frenkel exciton model by applying fragmentation-based electronic structure calculations to the output of classical molecular dynamics simulations. This methodology is inherently limited by the system size of the all-atom simulation, which is well below the performance capability of site-based models. Here, we demonstrate that this system size limitation can be effectively overcome by defining a size-extendable surrogate model based on the correlated parameter statistics derived from existing fragmentation-based methods. We demonstrate our approach on a monolayer film of sexithiophene molecules, first validating the accuracy of the surrogate system in reproducing exciton dynamical properties of a 150 molecule system, then extending it to systems of 2500 molecules. With this extended system, we explore the sensitivity of exciton dynamics to variations in the temperature as well as the amplitude and spatial correlations of energetic disorder. We conclude that exciton dynamics can be significantly enhanced in morphologies with spatially correlated molecular configurations but only if the overall distribution of site energies is sufficiently broad.