Roth, F.; Neppl, S.; Shavorskiy, A.; Arion, T.; Mahl, J.; Seo, H.; Bluhm, H.; Hussain, Z.; Gessner, O.; Eberhardt, W.: Efficient charge generation from triplet excitons in metal-organic heterojunctions. Physical Review B 99 (2019), p. 020303/1-6
The success of many emerging molecular electronics concepts hinges on an atomistic understanding ofthe 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–C60heterojunction. Contrary to common belief, fast intersystem crossing to triplet excitonsafter photoexcitation is not a loss channel but contributes to a significantly larger extent to the time-integratedinterfacial charge generation than the initially excited singlet excitons. The tr-XPS data provide direct access tothe diffusivity of the triplet excitonsDCuPc=(1.8±1.2)×10−5cm2/s (where CuPc is copper-phthalocyanine)and their diffusion lengthLdiff=(8±3) nm.