Singlet fission (SF) holds the promise for enabling organic photovoltaic systems to exceed the Shockley-Queisser limit by generating two triplet excitons from one absorbing photon. The rate of the SF process is a key parameter for designing photovoltaic devices utilizing this mechanism, not only for the efficient generation of triplet excitons, but also for preventing direct electron transfer from singlet excited states before SF. The present study demonstrates that the rate of SF of a pentacene derivative, 6,13-dipenylpentacene (DPP), can be mediated by forming co-aggregates with PbS quantum dots (QDs) in aqueous solutions. The SF rate shows a strong dependence on the sizes of co-aggregated PbS QDs. When co-aggregated with QDs that have a size of r=2.2 nm, the SF can be accelerated by six-fold compared to that in pure DPP aggregates. Using dynamic light scattering, electron microscopy and X-ray diffraction, the structure of the QD-DPP assemblies is characterized. The change of the SF rate is attributed to the disturbance of the packing of DPP molecules in the aggregates, which affects the electronic coupling between the singlet and the triplet excited states. This weak disturbance is caused by the interaction between DPP molecules and the surface ligand, poly(ethylene glycol) thiolate, and its effect on SF is prominent. The result sheds light on the fundamental mechanism of SF, and provides a possible way to boost the overall efficiency of an SF devices using PbS QDs as electron acceptors.

Mediating the rates of singlet fission in 6,13-dipenylpentacene aggregates with PbS quantum dots

255th National Meeting (2018)

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