Nanoscale Visualization of Photodegradation Dynamics of MAPbI₃ Perovskite Films

Herein, we report the nanoscale visualization of the photochemical degradation dynamics of MAPbI₃ (MA = CH₃NH₃⁺) using infrared scattering scanning near-field microscopy (IR s-SNOM) combined with a series of complementary analytical techniques such as UV-vis and FTIR-spectroscopy, XRD, and XPS. Light exposure of the MAPbI₃ films resulted in a gradual loss of MA⁺ cations starting from the grain boundaries at the film surface and slowly progressing toward the center of the grains and deeper into the bulk perovskite phase. The binary lead iodide PbI₂ was found to be the major perovskite photochemical degradation product under the experimental conditions used. Interestingly, the formation of the PbI₂ skin over the perovskite grains resulted in a largely enhanced photoluminescence, which resembles the effects observed for core-shell quantum dots. The obtained results demonstrate that IR s-SNOM represents a powerful technique for studying the spatially resolved degradation dynamics of perovskite absorbers and revealing the associated material aging pathways.