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Open Access Publications from the University of California

Efficient charge generation from triplet excitons in metal-organic heterojunctions


The success of many emerging molecular electronics concepts hinges on an atomistic understanding of the underlying electronic dynamics. We employ picosecond time-resolved x-ray photoemission spectroscopy (tr-XPS) to elucidate the roles of singlet and triplet excitons for photoinduced charge generation at a copper-phthalocyanine-C60 heterojunction. Contrary to common belief, fast intersystem crossing to triplet excitons after photoexcitation is not a loss channel but contributes to a significantly larger extent to the time-integrated interfacial charge generation than the initially excited singlet excitons. The tr-XPS data provide direct access to the diffusivity of the triplet excitons DCuPc=(1.8±1.2)×10-5cm2/s (where CuPc is copper-phthalocyanine) and their diffusion length Ldiff=(8±3)nm.

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