Self-Healing Beyond Molecular Iodine Locking in Formamidinium Lead Triiodide Perovskites

Iodide-based perovskites commonly undergo irreversible decomposition under operational conditions due to molecular iodine (I2) generation, severely impacting device longevity. In this study, we introduce 1,4-dithiane (DT) as an efficient molecular iodine locking (MIL) agent at grain boundaries and surfaces of formamidinium lead triiodide (FAPbI3) perovskite absorbers. The incorporation of DT not only minimizes iodine evaporation through robust S···I halogen bonding but also facilitates the dissociation of I–I bonds, enabling dynamic self-healing of the δ-phase into the photoactive α-phase of FAPbI3 at room temperature. This “self-healing beyond MIL” mechanism ensures exceptional device stability under continuous light soaking (ISOS-L-1I), light–dark cycling (ISOS-LC-1I), and damp-heat stress (ISOS-D-3), with PSCs retaining >95% of their initial performance for 1000 h. The established iodine cycling process─comprising iodine capture, iodide regeneration, and vacancy backfilling─substantially enhances perovskite durability. Overall, this strategy presents a promising pathway for advancing robust PSCs and other iodine-sensitive optoelectronic devices.