Poly(3-alkylthiophene)-based diblock copolymers with controllable block lengths were synthesized by combining
Grignard metathesis (GRIM) method, Ni-catalyzed quasi-living polymerization and a subsequent azide-alkyne click
reaction to introduce a fullerene functionality into the side chains of one of the blocks. The fullerene-attached
copolymers had good solubility (> 30 g L<sup>-1</sup> in chlorobenzene) with high molecular weights (Mn > 20000). The diblock copolymer films showed the formation of clear nanostructures with the size of 20 nm in AFM phase image driven by the crystallization of poly(3-hexylthiophene) block and aggregation of the fullerene groups. The photovoltaic device based on the copolymers showed a power conversion efficiency of 2.5% with a much higher fill factor of 0.63 compared with the single component devices previously reported. These results indicate that the rational material designs enable to construct the donor-acceptor nanostructure suitable for the photovoltaic application without relying on the mixing of the materials.