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.