97 Full Paper Macromolecular Chemistry and Physics wileyonlinelibrary.com Macromol. Chem. Phys. 2012, 213, 97−107 © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/macp.201100547 Polystyrene-Based C 60 Acceptor Copolymers through Azide–Alkyne Click Chemistry Approaches Maria Heuken, Hartmut Komber, Brigitte Voit* Poly(styrene- r-propargyloxy styrene) with varying molecular weights is prepared by means of a nitroxide-mediated radical polymerization and a malonate is “clicked” to it. Fullerene C 60 is reacted under Bingel conditions with the polymer and can be covalently bound to its side chains. These polymers show good solubility in common organic solvents and intense studies are performed to deter- mine the degree of substitution with fullerenes. A loading of around 15 to 20 wt% is detected by thermogravimetric analyses (TGA). These materials might be promising as the acceptor component for donor–acceptor block copolymers. Furthermore, new bromine- and organo-azide-functionalized methano fullerenes are prepared and characterized. M. Heuken, H. Komber, B. Voit, Leibniz-Institut für Polymerforschung Dresden e.V., Hohe Strasse 6, 01069 Dresden, Germany E-mail: voit@ipfdd.de 1. Introduction Fullerenes and their derivatives have been intensively studied since their discovery by Kroto et al. in 1985 [1] and, probably even more important, since Krätschmer et al. [2] found a method to prepare them in a macroscopic scale. Because of their outstanding electrochemical properties, especially in terms of the electron-acceptor capability, their use in optoelectronic applications such as organic solar cells is of high interest. [3–7] The most studied concept for these solar cells is the bulk-heterojunction approach, where a combination of poly(3-hexylthiophene) (P3HT) and phenyl- C 61 -butyric acid methyl ester (PCBM) is a well-established system. Optimization of both material and processing con- ditions led to power conversion efficiencies (PCE) of around 5%. [8–10] Combining more elaborate materials, this bench- mark value could be raised recently to over 7%. [11] How- ever, these P3HT/PCBM blends are thermodynamically instable and macrophase separation occurs under exposure to sunlight over time. Considering that the domain size in solar cells should not exceed the exciton diffusion length of around 10 nm, [12] the formation of macrophases lowers the PCE significantly. On this account, rod-coil block copolymers combining donor and acceptor proper- ties often based on P3HT and a fullerene-functionalized polymer segment with defined properties came into focus. Block copolymers are well-studied systems, allow phase separation in the nanoscale and are effective compati- bilizers in blends. [13–15] Thus, the use of donor–acceptor block copolymers as surfactants in P3HT/PCBM blends is expected to have a stabilizing effect on the morphology enhancing the long-term stability. Some groups already proved a positive effect of block copolymers in this regard. Jo and co-workers [16] synthesized a diblock copolymer with P3HT and a fullerene-containing methacrylate block. They showed that the photoluminescence quenching for P3HT/PCBM blends containing a few percent of this block copolymer as surfactant was much better than for the pure blend, indicating a more efficient charge transfer. Fréchet and co-workers [17] designed a block copolymer via ring opening metathesis polymerization with side chains com- prising oligothiophene and C 60 . By this, they enhanced the stability of the P3HT/PCBM blend morphologies signifi- cantly. The addition of a compatibilizer was even shown to