Dynamics of Electron–Hole Coulomb Attractive Energy and Dipole Moment of Hot Excitons in Donor–Acceptor Polymers

Understanding charge separation processes after photoexcitation in organic photovoltaics is of great importance for optimizing device performance. Many studies have associated a polaron-pair or intrachain charge transfer state in organic polymers with an increased charge separation efficiency. It is then natural to ask how the chemical structure influences charge separation, enabling a more targeted material design. Here, we report on nonadiabatic ab initio molecular dynamics simulations of the hot exciton dynamics following photoexcitation for a series of donor–acceptor polymers. We provide detailed insights into the Coulomb attractive energy and the dynamical evolution of dipole moments in the excited states. The former is correlated with polaron-pair recombination, thus preventing charge separation; the latter is a potential enabler of charge separation. We calculate the ultrafast dynamics of these relatively simple charge-separation-efficiency quantifiers, correlate them with the underlying chemical structure, and relate them to their static counterparts in statistical ensembles. Our work provides an ensemble description of the dynamic process of the photoexcited polaron formation and solidifies the role of Coulomb attractive energy and excited state dipole moment as the descriptors of this process on a microscopic level.