Carrier dynamics in pentacene-perfluropentacene heterocrystals (Conference Presentation)

Aromatic molecules are among the most promising materials in the field of organic optoelectronic due to the favorable properties of the delocalized -electron system present in those molecules. One of the most studied systems in this material class is the planar molecule of pentacene. An interesting application for pentacene is the incorporation into a donor-acceptor heterojunction in combination with its perfluorinated counterpart. Such samples may be deposited as intermixed blends (molecular alloys) or as alternating layered stacks. The out-of-plane delocalized -electron systems cause significant intermolecular coupling, even enabling the formation of charge-transfer excitons across heterointerfaces. Hence, studying this model system forms the optimal platform to investigate excitation transfer and charge separation in organic solar cells. We present a comprehensive study of the optical properties of pentacene -perfluoropentacene heterosystems. The samples are grown as crystalline thin films in different molecular configurations: either layered or as intermixed blends, both, in standing and lying molecular orientation. Time resolved luminescence and linear absorption spectroscopy are performed to obtain the carrier dynamics of the charge transfer states and response of the pure materials. The influence of different packing motifs on the optical properties is investigated, revealing a radiationless long-range energy transfer in addition to the local occupation of charge-transfer states.