From Photo-Damage to Self-Healing in Thin Film Pb-Iodide Perovskites: Action at a Distance

Lead halide perovskites (HaPs) have gained much attention, especially for use in photovoltaics and optoelectronic devices. However, stability remains the major roadblock to implementing HaP-based devices. Self-healing, the material's intrinsic tendency to recover from damage without any external aid, is observed in HaPs. Yet, understanding of its detailed mechanism is still lacking. Fluorescence recovery after photobleaching and photoluminescence (PL) imaging are used to monitor changes in HaP polycrystalline thin films in both space and time following damage, through the self-recovery path. Changes in PL outside the excitation spot are identified immediately following photodamage for both CsPbI₃ (CsPI), showing photo-darkening, and MAPbI₃ (MAPI), exhibiting photo-brightening. During self-healing of the directly illuminated spot, MAPI peripheral fluorescence decreases to its initial level, whereas CsPI exhibits photo-brightening to above the original level. This can be correlated with processes occurring on two time scales: rapid electronic defect passivation and slower ion migration. Investigating PL dynamics under intense laser damage demonstrates that changes to PL can be attributed to a combination of charge carrier trapping and trap removal in the early stages and ion migration and redox reactions in later stages. The understanding of spatio-temporal dynamics of damage and self-healing can promote longevity of HaP-based devices.