  The stability of CH3NH3PbI3 was investigated by observing the damage on a
co-evaporated film irradiated by a blue laser in ultrahigh vacuum. X-ray
photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were
employed to investigate the irradiation effects on the surface. The core levels
of perovskite were observed to shift toward higher binding energy (BE) during
the irradiation, suggesting that surface became more n-type. Metallic Pb
appeared after 120 minutes of irradiation, indicating that the film has started
to decompose. The decomposition saturated after about 480 minutes of
irradiation when the ratio of metallic Pb to total Pb was about 33%.
Furthermore, the film was no longer continuous after irradiation because of the
stress change after irradiation, as the substrate Au and oxygen were detected
by XPS. SEM images also show a roughened surface after irradiation. The results
strongly indicate that the perovskite is sensitive to the laser irradiation,
and the decomposition is a self-limiting process.
