Nano-structuring polymer/fullerene composites through the interplay of conjugated polymer crystallization, block copolymer self-assembly and complementary hydrogen bonding interactions
We describe a facile strategy of precisely nano-structuring conjugated polymer (CP)/fullerene composites for organic photovoltaics (OPVs). By building in strong complementary hydrogen bonding interactions between CP nanofibers (NFs) and fullerene derivatives, well-defined and stable supramolecular polymer/fullerene composite NFs are obtained. Specifically, a conjugated block copolymer having poly(3-hexylthiophene) (P3HT) backbone selectively functionalized with polar isoorotic acid moieties, P3HT-b-P3IOAT, and a diaminopyridine tethered fullerene derivative, PCBP, are used as the building blocks. Self-assembly of P3HT-b-P3IOAT in mixed solvents leads to core–shell micelle-like NFs having IOA groups preferentially located on the periphery of the P3HT NF core, onto which PCBP molecules are subsequently attached non-covalently. Formation of such complex structures are studied in detail and confirmed by NMR spectroscopy, absorption spectroscopy, transmission electron microscopy, atomic force microscopy, and X-ray scattering measurements. Application of these composite NFs in OPV devices is investigated and evaluated, which shows close correlations between device performance and morphology controllability.