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Photoexcitation Dynamics in Films of C-60 and Zn Phthalocyanine with a Layered Nanostructure

Lane, Paul A.
Cunningham, Paul D.
Melinger, Joseph S.
Kushto, Gary P.
Esentürk, Okan
Heilweil, Edwin J.
We elucidate photoexcitation dynamics in C-60 and zinc phthalocyanine (ZnPc) from picoseconds to milliseconds by transient absorption and time-resolved terahertz spectroscopy. Autoionization of C-60 is a precursor to photocarrier generation. Decay of the terahertz signal is due to decreasing photocarrier mobility over the first 20 ps and thereafter reflects recombination dynamics. Singlet diffusion rates in C-60 are determined by modeling the rise of ground state bleaching of ZnPc absorption following C-60 excitation. Recombination dynamics transform from bimolecular to monomolecular as the layer thickness is reduced, revealing a metastable exciplex at the C-60/ZnPc interface with a lifetime of 150 mu s.