Super-Resolution Luminescence Microspectroscopy Reveals the Mechanism of Photoinduced Degradation in CH₃NH₃PbI₃ Perovskite Nanocrystals

Photoinduced degradation of individual methylammonium lead triiodide (MAPbI₃) perovskite nanocrystals was studied using super-resolution luminescence microspectroscopy under intense light excitation. The photoluminescence (PL) intensity decrease and blue-shift of the PL spectrum up to 60 nm together with spatial shifts in the emission localization position up to a few hundred nanometers were visualized in real time. PL blinking was found to temporarily suspend the degradation process, indicating that the degradation needs a high concentration of mobile photogenerated charges to occur. We propose that the mechanistic process of degradation occurs as the three-dimensional MAPbI₃ crystal structure smoothly collapses to the two-dimensional layered PbI₂ structure. The degradation starts locally and then spreads over the whole crystal. The structural collapse is primarily due to migration of methylammonium ions (MA⁺), which distorts the lattice structure causing alterations to the Pb–I–Pb bond angle and in turn changes the effective band gap