A Nonfullerene Acceptor Containing Rhodanine and Barbituric Acid End Groups for Use in Organic Photovoltaic Devices

We synthesized a rod-shaped asymmetric bithiophene-based nonfullerene small-molecule acceptor, ORH-T2-OBAR, for organic photovoltaic (OPV) cells. Electron-withdrawing rhodanine (RH) and barbituric acid (BAR) dye groups with long octyl side chains were asymmetrically introduced at either end. ORH-T2-OBAR exhibits thermal stability and solubility sufficient for fabricating OPVs. A blue-shifted absorption maximum at 440 nm and H-type aggregation are observed in the ORH-T2-OBAR film compared with ORH-T2-OBAR in solution. ORH-T2-OBAR has the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels as low as −3.63 eV and −5.81 eV, respectively, leading to sufficient energy offsets with the PTB7-Th polymer donor (LUMO = −3.19 eV, HOMO = −5.23 eV) to achieve exciton dissociation. Lastly, an inverted as-cast device fabricated with PTB7-Th and ORH-T2-OBAR as a donor and an acceptor, respectively, displayed a power conversion efficiency of 0.91%, an open-circuit voltage of 0.81 V, and an energy loss of 0.78 eV.