Benzocyclobutene-fullerene bisadducts as novel electron acceptors for enhancing open-circuit voltage in polymer solar cells

A novel 56 π-electron fullerene acceptor material, benzocyclobutene-C60 bisadducts (BCBCBA), was developed via the [2+2] cycloaddition of in-situ generated benzyne with C60 to raise the lowest unoccupied molecular orbital (LUMO) energy level of the fullerene. This four-membered linkages to C60 of BCBCBA resulted in the fullerene bisadducts with very addends, thus minimizing the adverse effects of their regioisomers on the intermolecular packing between fullerene bisadducts. In addition, the LUMO level of BCBCBA was as high as −3.70eV, which is 0.16eV higher than that of phenyl-C61-butyric acid methyl ester (PCBM) (−3.86eV). This result indicates the significant potential for improving open-circuit voltage (VOC) values in polymer solar cells (PSCs). The poly(3-hexylthiophene) (P3HT):BCBCBA based PSCs show VOC of 0.73 and power conversion efficiency (PCE) of 3.51%, which are similar to the P3HT:bis-PCBM based PSCs.