Capturing transiently charged states at the C60/TiO2(110) interface by time-resolved soft X-ray photoelectron spectroscopy

Time-resolved soft X-ray photoelectron spectroscopy is utilized to determine an energy level alignment and the photoexcited carrier dynamics at a C-60/TiO2(110) interface. The interface electronic structure is characterized by a type II junction, which favors an injection of photoexcited electrons from C-60 to TiO2. Ultraviolet (UV) laser pulse irradiation induces transient shifts of both C 1s and Ti 2p core levels towards the higher binding energies. These energy shifts are caused by a laser-induced charge transfer between the C-60 layer and the TiO2(110) surface. Upon UV absorption, valence electrons of C-60 are promoted to unoccupied levels, followed by a resonant transfer to TiO2, leaving C-60 in a cationized state. On the TiO2(110) side, the electrons are injected into the conduction band to raise the carrier density so that downward bending of the TiO2 band is induced. The UV-excited states of C-60 and TiO2 have sufficiently longer lifetime than the lifetime of the electron-hole pairs in solid C-60. The C-60/TiO2(110) interface is, thus, proved to be efficient for separating the electronehole pairs generated within the C-60 layer. (c) 2016 Elsevier B.V. All rights reserved.