Surface hopping simulations on charge photogeneration in conjugated polymers

The mechanism of charge photogeneration in neat conjugated polymers has long been controversial and a unified explanation has not been achieved so far. In this paper, we use a surface hopping method to simulate the excited-state dynamics of a system composed of five π-stacked polymer chains. In this system, polaron pairs (PPs) with large electron-hole distance can be seen as free charges. The surface hopping method is based on the Pariser-Parr-Pople (PPP) Hamiltonian and the excited states of the system are calculated with configuration interaction singles (CIS) formalism. During the simulations, the yields of PPs and free charges are calculated using a statistical method. By comparison, it is found that impurity and excess energy have significant effects on the yields of PPs and free charges. Free charges are difficult to be generated in neat systems with small excess energy. Free charges come from direct dissociation of high-energy excitons.