Photovoltaic and charge transfer analysis of perylene diimide dimer systems

The dimerization of perylene diimide (PDI) with a bridge separating each monomer has been of interest recently due to notable increases in device efficiencies. We aim to further investigate the impact this bridge has on the photovoltaic and charge transfer properties of an organic photovoltaic using electronic structure methods. Calculations were performed on a variety of heteroatom substituted bridge units in both fused and unfused PDI dimers to directly compare with the previously studied thiophene bridge unit. The systems consist of bridged PDI dimers as an acceptor, coupled with a known polymer donor. Using Marcus theory, the rates of intermolecular charge recombination (k(CR)) and charge transfer (k(CT)) were calculated using the Gibbs free energies, reorganization energy and electronic coupling for each system. Fused systems exhibit a k(CT)/k(CR )ratio up to 10(6) times higher than unfused systems, decreased reorganization energy, and had more favorable Gibbs free energies. Larger heteroatom substitutions, like silicon and phosphorus, have improved photovoltaic and Marcus theory parameters, and show potential to perform better than typical thiophene linkers.