Table in the Supplementary Information. The NA-AIMD simulations employ trajectory surface hopping with fewest switching criterion. Nonadiabatic couplings are evaluated based on wavefunction overlaps, which was already used for NA-AIMD simulations of oligotiophenes. A time step of 0.5 fs was employed in combination with a screening threshold features qualitatively well. PCPDT-BT I features one main peak at around 2.22 eV with a shoulder peak at around 3.06 eV, a second peak at around 3.69 eV, and a third peak at around 4.52 eV. We note that the absolute values of the excitation energies depend much on the method used and are not directly comparable to the experiment. However, the relative state ordering and arrangement are typically well described by the method used. By increasing the spacing between the donor and acceptor unit by a π-linker, i.e., polymer PCPDT-2TBT, the main absorption peak shifts by about 0.19 eV to slightly higher energy (around 2.41 eV) and the second peak shifts by around 0.39 eV to slightly lower energy around 3.30 eV appearing as a shoulder of the main peak. Both shifts are qualitatively in good agreement with experiment and decrease the energy gap between the main peak and second peak. The third peak is almost unaffected by the increased distance between the donor and acceptor unit. Increasing the electron affinity of the acceptor unit, i.e., polymer PCPDT-BDT, the absorption spectrum changes fundamentally. A main peak appears at 1.02 eV and a second peak at 1.88 eV. Moreover, a broad absorption band at higher energies with a maximum at 3.17 eV is formed. Increasing the acceptor unit size, i.e., model polymer PCPDT-BT II, the main peak shifts slightly to higher energy (2.34 eV). The second peak is reduced in amplitude and shifted to slightly higher energy at around 3.82 eV. The third peak is almost unaffected similar to the π-linker polymer.