Unveiling the Electronic Structure of ZnO–C60 Core–Shell Quantum Dots: The Origin of Efficient Electron Transport

Abstract

The electronic structure of ZnO core–C60 shell (ZnO@C60) quantum dots (QDs) was investigated with the help of model interface analysis between ZnO QDs and C60 using in situ ultraviolet and X-ray photoelectron spectroscopy measurements. To form the ZnO QDs/C60 interface in situ, a vacuum-integrated electrospray deposition technique was employed to simulate the electronic interactions between ZnO QDs and C60 upon the formation of a ZnO@C60 core–shell structure. Photoelectron spectra of ZnO QDs/C60 interface formation were compared with those of ZnO@C60 QD and pristine ZnO QD films. The results revealed that ZnO QDs and C60 interacted via electron transfer leading to the change in ionization energy of the surface C60. This induced a negligible energy barrier between the lowest unoccupied molecular orbital level of C60 and the conduction band minimum of ZnO, which led to efficient electron transport through the ZnO@C60 QDs.