Deciphering the Structure of PM6-Type Conjugated Polymer Aggregates in Solution and Film

The morphology of conjugated polymer films is highly tunable, influencing their performance in organic electronics. Specifically, the molecular packing or crystal structure strongly influences electronic processes such as light absorption and charge transfer. However, the unit cells of high-performance electron donor polymers remain unknown, limiting our understanding of how processing affects structure and device performance. This study characterizes the aggregate structure of PM6-type push–pull polymers by using X-ray scattering, cryogenic electron microscopy, and molecular dynamics (MD) simulations. A forward simulation approach linking grazing-incidence wide-angle X-ray scattering (GIWAXS) with MD resolves a monoclinic unit cell that accurately describes PM6-type polymer aggregates in both thin films and casting solutions. Intimate π–π stacking between the donor and acceptor units emerges from this unit cell. Analysis of experimental GIWAXS using this unit cell quantifies sliding disorder in these aggregates, which may impact device performance. The shape and internal structure of the solution aggregates are also identified in chlorobenzene. These findings enhance our understanding of PM6-type polymer packing and outline a strategy for elucidating the crystal structures of weakly ordered materials. We expect that these results will provide future opportunities to control optoelectronic performance through aggregate formation in PM6 and other push–pull conjugated polymers.