These results indicate a competition between the charge separation process via a highly polarized ICT or polaron-pair state, which correlates to the dipole moment, and the CAE as attractive interaction between the electron and hole to recombine. While the former needs to be comparably high to spatially separate the electron and hole the latter should be reduced simultaneously. A possible route to achieve a polymer featuring these two properties is to increase the size of the acceptor unit instead of increasing the electron affinity of the acceptor unit (e.g., via the BDT acceptor unit). The idea is that, while a delocalized hole wavefunction reduces the recombination rate of the polaron-pair, π-spacer for a hot exciton may originate from the fact that the extension of the acceptor unit not only increases the backbone of the acceptor unit, but also increases the interaction of the electron wavefunction with the enhanced "pulling" effect of the N-substitutions, thus trapping the electron wavefunction. We note that lower energy excitons, i.e., only the lowest excited states, may exhibit different behavior for PCPDT-BT II. These insights indicate that there is a size-limit for the acceptor unit similar to a size-limit of the π-bridge to optimize the device performance thus providing new design rules to increase the polaron-pair separation. The optimized donor-acceptor polymer should have a donor and small acceptor unit well separated by a π-bridge with the acceptor unit's electron affinity being high enough to produce a strongly polarized excited state, but not so high as to allow recombination due to strong Coulomb interaction of the excited electron and hole.