Multiscale study of the influence of the chemical structure on exciton dynamics in polymeric systems

Abstract

One of the milestones in the photovoltaic field was the use of a bulk-heterojunction made of polymer/low weight molecules to increase organic solar cells efficiency. When an exciton is created in the polymer, it can easily be dissociated into an electron/hole pair if the exciton reaches the polymer/low weight molecule interface. For that happens, it is necessary an efficient exciton diffusion towards the interface before it decays. This process depends on the polymer used, since it will affect the exciton dynamics, as it is suggested from the experiments. However, there is not a clear relationship between the polymer molecular structure and the exciton dynamics. In this communication we present a study of the influence of polymer molecular properties on exciton dynamics using a multiscale model. We use quantum molecular dynamic calculations to understand the effect of polymer molecular properties on singlet exciton formation in polymeric systems, since they are the main excited species produced in polymer-based solar cells. The results obtained where used as input parameters in a dynamic Monte Carlo simulations to study the singlet exciton dynamics in polymeric systems. Understand the influence of the polymer morphology on exciton dynamics within the device. The results obtained clearly show that the polymer chemical structure influences not only the intramolecular singlet exciton energy but also it will influence the exciton diffusion process in the polymer network.