Evolution of Chemical Composition, Morphology, and Photovoltaic Efficiency of CH₃NH₃PbI₃ Perovskite under Ambient Conditions

The surface composition and morphology of CH 3 NH 3 PbI 3 perovskite films stored for several days under ambient conditions were investigated by X-ray photoelectron spectroscopy, scanning electron microscopy, and X-ray diffraction techniques. Chemical analysis revealed the loss of CH 3 NH 3 + and I – species from CH 3 NH 3 PbI 3 and its subsequent decomposition into lead carbonate, lead hydroxide, and lead oxide. After long-term storage under ambient conditions, morphological analysis revealed the transformation of randomly distributed defects and cracks, initially present in the densely packed crystalline structure, into relatively small grains. In contrast to PbI 2 powder, CH 3 NH 3 PbI 3 exhibited a different degradation trend under ambient conditions. Therefore, we propose a plausible CH 3 NH 3 PbI 3 decomposition pathway that explains the changes in the chemical composition of CH 3 NH 3 PbI 3 under ambient conditions. In addition, films stored under such conditions were incorporated into photovoltaic cells, and their performances were examined. The chemical changes in the decomposed films were found to cause a significant decrease in the photovoltaic efficiency of CH 3 NH 3 PbI 3 .