Conjugated Polymer/Fullerene Nanostructures through Cooperative Non-Covalent Interactions for Organic Solar Cells

We have previously reported the formation of polymer/fullerene core–shell composite nanofibers (NFs) through self-assembly of functionalized conjugated block copolymers and fullerene derivatives, by cooperation of orthogonal non-covalent interactions including block copolymer phase separation, fullerene aggregation, poly(3-hexylthiophene) (P3HT) crystallization and complementary hydrogen bonding. These NFs displayed improved solar cell performances and the core–shell type structures are generally insensitive to polymer/fullerene weight ratios. In order to better understand the self-assembly mechanisms of such complex systems, we have prepared a new block copolymer (P3) having a different block length ratio and studied its solution and thin film morphologies in the presence of fullerene derivatives at different weight ratios. Worm-like micelles are observed for P3 in mixed-solvent solutions, distinctly different from the well-defined NFs observed previously. Upon fullerene additions, the solution morphologies gradually change into hierarchically complex nanostructures with varying fullerene contents. Thin film morphologies are studied by atomic force microscopy (AFM) and the blends are applied in organic solar cell (OSC) devices. Our present studies provide detailed information on the self-assembly behaviors of conjugated block copolymers and fullerenes under cooperative orthogonal non-covalent interactions.