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

Understanding charge separation processes after photo-excitation 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 increased charge separation efficiency. It is then natural to ask how the chemical structure influences charge separation, enabling a more targeted materials design. Here, we report on non-adiabatic ab-initio molecular dynamics simulations of the hot exciton dynamics following photo-excitation for a series of donor-acceptor polymers. We provide detailed insights into Coulomb attractive energy and 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. The insights obtained here can be extended to more complex molecular compound scenarios and will inform future optimization of materials and device performance.