[70]fullerene-based materials for organic solar cells.

The synthesis, characterization and photovoltaic study of two novel derivatives of [70]fullerene, phenyl-C₇₁-propionic acid propyl ester ([70]PCPP) and phenyl-C₇₁-propionic acid butyl ester ([70]PCPB), are reported. [70]PCPP and [70]PCPB outperform the conventional material (6,6)-phenyl-C₇₁-butyric acid methyl ester ([70]PCBM) in solar cells based on poly(2-methoxy-5-{3',7'-dimethyloctyloxy}-p-phenylene vinylene) (MDMO-PPV) as a donor polymer using chlorobenzene (CB) or dichlorobenzene (DCB) as solvents. AFM data suggest that improvement of the device efficiency should be attributed to the increased phase compatibility between the novel C₇₀ derivatives and the polymer matrix. [70]PCPP and [70]PCBM showed more or less equally high performances in solar cells comprising poly(3-hexylthiophene) (P3HT) as a donor polymer. Optical modeling revealed that the application of [70]fullerene derivatives as acceptor materials in P3HT-based bulk heterojunction solar cells might give approximately 10 % higher short circuit current densities than using C₆₀-based materials such as [60]PCBM. The high solubility of [70]PCPP and [70]PCPB and their good compatibility with the donor polymers suggest these fullerene derivatives as promising electron acceptor materials for use in efficient bulk heterojunction organic solar cells.