Photodegradation pathways of CH3NH3PbI3 organic perovskite polycrystalline film observed by in-situ scanning probe microscopy

[Display omitted] •The stray laser effect of SPM is able to affect the degradation pathway in MAPbI3.•Several hours is sufficient for MAPbI3 film to undergo red light degradation in N2.•Hydrate did not occur during photodegradation even in the presence of H2O. In this study, the in-situ observation of degradation-induced local elastic modulus (Young’s modulus) variation in CH3NH3PbI3 (MAPbI3) polycrystalline film was conducted using the continuous scanning by scanning probe microscopy (SPM). We pointed out that the observed degradation in MAPbI3 film under the SPM continuous scanning is a photo-excited process due to the stray laser effect induced by the scattering of the SPM-equipped red laser. The degradation rate was highly accelerated by light illumination when the MAPbI3 polycrystalline films were aged in humid air, O2, dry air, and N2 atmosphere. Significantly, the SPM analysis result shows that several hours is sufficient for MAPbI3 film to undergo red light degradation in N2. Otherwise, under light illumination, the result provides evidence that hydrate, which is the critical intermediate phase to trigger humid degradation, did not occur even in the presence of H2O. It identifies H2O is not the preferential species to react with the photo-excited MAPbI3. Though the laser effect must be carefully taken into account, this study indicates that SPM is an appropriate analysis technique to examine the infinitesimal variation of surface property in organic perovskite material, clarifying the degradation mechanism in the initial period.