Interface electronic properties of co-evaporated MAPbI_3 on ZnO(0001): In situ X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy study

摘要

In this work, the interface electronic properties of ZnO(0001)/CH_3NH_3PbI_3 were investigated by both X-ray and ultraviolet photoelectron spectroscopy. The CH_3NH_3PbI_3 thin films were grown on single crystalline ZnO(0001) substrate in situ by co-evaporation of PbI_2 and CH_3NH_3I 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 CH_3NH_3PbI_3, while the valence band maximum of ZnO lies 2.1 eV below that of CH_3NH_3PbI_3, implying that the electrons can be effectively transported from CH_3NH_3PbI_3 to ZnO, and the holes can be blocked in the same time. A PbI_2 rich layer was initially formed at the interface of ZnO(0001)/CH_3NH_3PbI_3 during the growth. As a consequence, an interface barrier was built up which may prevent the electron transport at the interface.