Controlled Synthesis of Fullerene-Attached Poly(3-alkylthiophene)-Based Copolymers for Rational Morphological Design in Polymer Photovoltaic Devices

Abstract

Poly(3-alkylthiophene)-based diblock copolymers with controllable block lengths were synthesized by combining the Grignard metathesis 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–1 in chlorobenzene) with high molecular weights (Mn > 20 000). The diblock copolymer films formed clear nanostructures with sizes of ca. 20 nm, driven by crystallization of the poly(3-hexylthiophene) block and aggregation of the fullerene groups, as observed in AFM phase images. The copolymer-based photovoltaic device showed a power conversion efficiency of 2.5%, with a much higher fill factor of 0.63 in comparison to the previously reported single component devices. These results indicate that rational material designs enable the construction of suitable donor–acceptor nanostructures for photovoltaic applications, without relying on the mixing of materials.