Y6 is a high-performance non-fullerene acceptor widely used in organic solar cells. The assembly behavior of Y6 at interfaces, however, remains mostly unknown and respective in-depth investigations are missing. Here, we use room temperature scanning tunneling microscopy to investigate the self-assembly of Y6 at the solid–liquid interface. We show how coadsorption of polycyclic aromatic hydrocarbon donor molecules leads to the formation of a series of donor–acceptor interfacial cocrystals with tailored molecular structure and order on a graphite surface. The gained understanding of the intricate interplay of the underlying intermolecular interactions should facilitate the engineering of multicomponent interfacial nanostructures and help to potentially improve charge separation and transport in organic (opto)electronic devices.