Interfacial Molecular Packing Determines Exciton Dynamics in Molecular Heterostructures: The Case of Pentacene–Perfluoropentacene

The great majority of electronic and optoelectronic devices depend on interfaces between p-type and n-type semiconductors. Finding matching donor–acceptor systems in molecular semiconductors remains a challenging endeavor because structurally compatible molecules may not necessarily be suitable with respect to their optical and electronic properties, and the large exciton binding energy in these materials may favor bound electron–hole pairs rather than free carriers or charge transfer at an interface. Regardless, interfacial charge-transfer exciton states are commonly considered as an intermediate step to achieve exciton dissociation. The formation efficiency and decay dynamics of such states will strongly depend on the molecular makeup of the interface, especially the relative alignment of donor and acceptor molecules. Structurally well-defined pentacene–perfluoropentacene heterostructures of different molecular orientations are virtually ideal model systems to study the interrelation between molecular p...