Unraveling the light-induced degradation mechanism of CH3NH3PbI3 perovskite films

Abstract

Abstract While metal halide hybrid perovskite solar cells (PeSCs) are remarkably efficient, the rapid and undesirable degradation limit their practical applications for renewable energy sources. Herein, the evolution of perovskite decomposition under white light illumination has been investigated under the ultrahigh vacuum conditions, which can effectively rule out the influence of other factors such as oxygen or moisture. The chemical composition, electronic structure, surface morphology, and crystal structure of CH3NH3PbI3 perovskite films have been systematically characterized by X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS), scanning electron microscopy, and X-ray diffraction techniques. The surface roughening with cracks and defects occurs in CH3NH3PbI3 perovskite films after a short-time white-light illumination in ultrahigh vacuum. In situ compositional analysis reveals the decomposition of the perovskite films with the appearance of metallic Pb feature, which is accompanied with the energy level shift towards higher binding energy during the illumination process. However, the decomposition rate is decreased and becomes saturated after exposed to light illumination for 24 h. These findings provide a direct evidence that CH3NH3PbI3 perovskite is photosensitive, and a light-induced degradation mechanism is proposed.