Photoinduced C70 radical anions in polymer:fullerene blends

Photoinduced polarons in solid films of polymer-fullerene blends were studied by photoluminescence (PL), photoinduced absorption (PIA) and electron spin resonance (ESR). The donor materials used were P3HT and MEH-PPV. As acceptors we employed PC60BM as reference and various soluble C70-derivates: PC70BM, two different diphenylmethano-[70]fullerene oligoether (C70-DPM-OE) and two dimers, C70-C70 and C60-C70. Blend films containing C70 revealed characteristic spectroscopic signatures not seen with C60. Light-induced ESR showed signals at g\geq2.005, assigned to an electron localized on the C70 cage. The formation of C70 radical anions also leads to a subgap PIA band at 0.92 eV, hidden in the spectra of C70-based P3HT and MEH-PPV blends, which allows for more exact studies of charge separated states in conjugated polymer:C70 blends.