Interface electronic properties of co-evaporated MAPbI₃ on ZnO(0001): In situ X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy study

In this work, the interface electronic properties of ZnO(0001)/CH₃NH₃PbI₃ were investigated by both X-ray and ultraviolet photoelectron spectroscopy. The CH₃NH₃PbI₃ thin films were grown on single crystalline ZnO(0001) substrate in situ by co-evaporation of PbI₂ and CH₃NH₃I at room temperature with various thickness from 1.5 nm to 190 nm. It was found that the conduction band minimum of ZnO lies 0.3 eV below that of CH₃NH₃PbI₃, while the valence band maximum of ZnO lies 2.1 eV below that of CH₃NH₃PbI₃, implying that the electrons can be effectively transported from CH₃NH₃PbI₃ to ZnO, and the holes can be blocked in the same time. A PbI₂ rich layer was initially formed at the interface of ZnO(0001)/CH₃NH₃PbI₃ during the growth. As a consequence, an interface barrier was built up which may prevent the electron transport at the interface.