Metal Halide Perovskites Demonstrate Radiation Hardness and Defect Healing in Vacuum

Area of Science:

• Materials Science
• Solid-State Chemistry
• Photovoltaics

Background:

• Formamidinium lead iodide (FAPbI3) is a key material in perovskite solar cells.
• Understanding FAPbI3 degradation under operational stress is crucial for device stability.

Purpose of the Study:

• To investigate the structural and chemical changes in FAPbI3 films under X-ray irradiation and various atmospheric conditions.
• To elucidate the mechanisms of perovskite degradation and identify potential self-healing pathways.

Main Methods:

• X-ray diffraction (XRD) was used to monitor changes in the FAPbI3 lattice structure.
• Experiments were conducted under controlled atmospheres (O2, He, Ar, N2, vacuum) at 75 °C with Cu Kα X-ray irradiation.
• Density functional theory (DFT) calculations using GGA-PBE were employed to simulate defect interactions.

Main Results:

• Irradiation induced a reproducible perovskite lattice contraction (1.1 ± 0.5 Å3) and concurrent perovskite loss with lead iodide growth under all tested gas conditions.
• Oxygen-containing gases accelerated degradation rates but did not alter the fundamental perovskite structural changes.
• In vacuum, FAPbI3 films exhibited self-healing, characterized by lattice expansion (0.9 ± 0.3 Å3) and stabilization.
• Lattice contraction is linked to an increase in Schottky defects (formamidinium and iodine vacancies).

Conclusions:

• Perovskite degradation under irradiation involves the diffusion and precipitation of Schottky defects, forming lead iodide.
• Ionized gases exacerbate degradation by promoting the continuous loss of formamidinium and iodine ions.
• Vacuum conditions offer a promising avenue for stabilizing FAPbI3 by enabling defect self-healing.