Effects of Precursor Ratios and Annealing on Electronic Structure and Surface Composition of CH3NH3PbI3 Perovskite Films

The electronic structure and surface composition of CH3NH3PbI3 (MAPbI3) films fabricated by one-step method with different precursor ratios of PbI2 to CH3NH3I (PbI2/MAI) have been investigated with ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). It is found that the core levels of all components in the MAPbI3 film shift toward lower binding energy with decreasing the precursor ratio of PbI2/MAI, indicating that the electronic structures of the MAPbI3 film can be adjusted by the precursor ratio of PbI2/MAI. The elemental compositions of the MAPbI3 film also depend on the precursor ratio and annealing process, and the compositions are strongly correlated to the electronic properties of the films. The electronic properties remain unchanged with an annealing at 110 °C. However, a core level shift of 0.5 eV toward higher binding energy is observed with an annealing at 150 °C, together with noticeable composition change from the XPS core level analysis. The distribution of all chemical components in the MAPbI3 film is further investigated with angle-resolved XPS (AR-XPS). It is observed that annealing at 150 °C leads to relatively shallow distribution variations of I and Pb in the MAPbI3 film, accompanied by infiltration of metallic Pb into the bulk.