Photoinduced C₇₀ radical anions in polymer:fullerene blends

Abstract

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 ≥ 2.005, 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. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)