In addition to the intrachain electron transfer demonstrated above, a more common interpretation of Brønsted acid doping is the occurrence of an interchain electron transfer. To investigate this mechanism, a neutral PCPDT-BT tetramer (four repeat units) and a double protonated PCPDT-BT tetramer are brought in proximity to each other and the structure of the entire complex is optimized. The resulting optimized structure is shown in Fig. . In this structure an interchain electron transfer occurs that is manifested in a partial charge of each chain of about 1e and a broken spin symmetry with singly unoccupied molecular orbitals on the un-protonated chain, which resemble the signatures of a positive polaron as illustrated in Fig. . Similar to the intrachain electron transfer, a SOMO is found on the double protonated chain featuring localized antibonding character, as shown in Fig. . The occurrence of both intrachain and interchain electron transfer are in line with the pictures proposed in the literature. True interchain electron transfer is only observed for certain proton positions in our calculations and further depends on inter-molecular positioning. For other cases only charge transfer complex formation is found but no integer-charge transfer as reported in Fig. . These findings are also in agreement with previous reports on the coexistence of ICT and CTC in OSC materials doped with molecular dopants.