Oxygen Intercalation Induced by Photocatalysis on the Surface of Hybrid Lead Halide Perovskites

Methylammonium lead iodide (MAPbI(3)) perovskite has emerged as a dazzling nova in the solar cell realm. However, the robustness or stability of the material exposed to different ambiences is a key issue. In this paper, resonance Raman spectroscopy is combined with surface and bulk crystal characterizations to interpret the oxygen intercalation phenomenon on the surface of MAPbI(3). We observe that oxygen can intercalate into the frameworks of MAPbI(3) with the assistance of laser excitation. By lowering down the pressure in the experimental chamber, the intercalated oxygen can be readily removed. Xray photoelectron spectroscopy and X-ray diffraction characterizations suggest that Pb-O bonds are mainly formed on the surface of MAPbI(3) but are constrained to avoid the formation of PbO compound. The quantum chemical calculation based on density functional theory supports the above conclusions. The understanding of oxygen intercalation in MAPbI(3) shall benefit the improvement of stability of the important solar cell materials.