Effects of Intramolecular Donor-Acceptor Interactions on Bimolecular Recombination in Small-Molecule Organic Photovoltaic Cells

To enhance the device performance of bulk heterojunction organic photovoltaic (OPV) cells, recombination processes must be suppressed. Here, we prepared OPV cells using donor materials composed of different electron-rich donor and electron-deficient acceptor units and the acceptor material 6,6-phenyl-C61-butyric acid methyl ester. The effects of the polarization of the donor materials which was induced by the intramolecular donor-acceptor (D-A) interactions on the bimolecular recombination constant of each device were studied using a time-of-flight method. A large D-A interaction decreased the bimolecular recombination constant, increasing the fill factor of the device. An active layer with a large dielectric constant led to a small Coulomb capture radius between the radical cations and anions. Overall, a larger D-A interaction enhanced the device performance of small-molecule OPV cells.