Enhanced Photoresponsivity of Fullerene in the Presence of Phthalocyanine: A Time-Resolved X-ray Photoelectron Spectroscopy Study of Phthalocyanine/C60/TiO2(110)

Time-resolved soft X-ray photoelectron spectroscopy has been utilized to reveal a time evolution of excitation states of metal and metaloxo phthalocyanine (MPc; M = Cu and TiO) and fullerene (C-60) in the ultrathin layered MPc/C-60/TiO2(110) systems. C is core-level photoemission peaks of MPc and C-60 were monitored to assess spontaneous changes induced by ultraviolet laser. The C is peaks of both species move toward higher binding energies, reflecting cationization of the molecules as a result of dissociation of photoexcited excitons followed by electron transfer from the molecules to TiO2. The magnitude of the C-60 C is peak shift is as large as 13-14 meV, whereas the shift of only 7 meV is induced when phthalocyanine-free C-60/TiO2(110) is excited. Photoresponsivity of C-60 is enhanced when C-60 coexists with the phthalocyanine molecules. An efficient energy transfer from photoexcited MPc to C-60 and a resultant exciton formation in C-60 are responsible for this enhancement.