Doping efficiency and energy-level scheme in C60F48-doped zinc–tetraphenylporphyrin films

High resolution synchrotron-based core level spectroscopy was used to examine the energy level alignment at the interface of zinc–tetraphenylporphyrin films doped by the surface acceptor C60F48. Two distinct fluorofullerene charge states were identified, corresponding to ionized and neutral molecules, and their relative concentration as a function of coverage was used to evaluate the probability of occupation of the acceptor lowest unoccupied molecular orbital (LUMO). From an initial acceptor energy of −0.25 eV, the C60F48 LUMO shifts upwards with coverage due to a doping-induced interfacial dipole potential, and stabilization of the LUMO at an energy 0.45 eV above the Fermi energy was obtained. While the energy difference upon saturation is consistent with the results obtained for other donor–acceptor systems that have been interpreted as Fermi level pinning, the present work shows that the energy offset is a direct consequence of the interplay between Fermi–Dirac statistics in combination with the interfacial dipole potential.

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► The energy level alignment at the ZnTPP/C60F48 interface was experimentally investigated.
► Ionized and neutral C60F48 were identified using high-resolution photoelectron spectroscopy.
► The C60F48 acceptor state energy was determined from the experimentally evaluated doping efficiency.
► The energy offset is a consequence of the interplay between Fermi statistics in combination with an interfacial potential.