Methylammonium lead halide perovskites have been developed as highly promising
materials to fabricate efficient solar cells in the past few years. We have
investigated degradation of co-evaporated
CH3NH3PbI3 films in ambient air, oxygen and
water respectively using x-ray photoelectron spectroscopy (XPS), small angle
x-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron
microscopy (SEM). The CH3NH3PbI3 film has an
excellent atomic ratio and crystallinity. XPS results indicate that the film is
not sensitive to oxygen and dry air, while ambient and water exposures achieve
similar effects. XRD further indicates a structural conversion to
PbI2 and a drastic morphology change from smooth to rough is revealed
by AFM and SEM. The experiment indicated that H2O plays a dominated
role in the degradation of CH3NH3PbI3 films.
The degradation can be characterized by almost complete removal of N,
substantial reduction of I, residual of PbI2, C, O, and I compounds
on the surface.