External Electric Field-Dependent Photoinduced Charge Transfer in a Donor–Acceptor System for an Organic Solar Cell

External electric field is incorporated into the generalized Mulliken–Hush model and Marcus theory. With this new development, we have investigated the field-dependent electronic structure and rate of photoinduced charge transfer in organic donor–acceptor dyad using time-dependent density functional theory and extensive multidimensional visualization techniques. The model is used to evaluate the influence of the external electric field on the electronic coupling between donor and acceptor. The reorganization energy and the free energy change of the electron transfer were calculated. It was found that the major effects in the external electric field dependent rate of the charge transfer originate from changes in the electronic coupling. The new theoretical approach not only promotes a deeper understanding of the connection between the external electric field, chemical structure, and optical and electronic properties of the donor–acceptor system, but also can be used for rational design of novel donor–acceptor system for organic solar cells.