Metal Halide Perovskites Demonstrate Radiation Hardness and Defect Healing in Vacuum

Herein, we subject formamidinium
lead iodide films to oxygen-containing
gases (flowing O2 or free diffusion of lab atmosphere),
inert gases (flowing He, Ar, or N2), and vacuum. Our films
are irradiated by Cu Kα X-rays and held at 75 °C while
X-ray diffraction is recorded. Under all gas conditions, we observe
a reproducible 1.1 ± 0.5 Å3 perovskite lattice
contraction from an initial unit cell volume of 256.5 ± 0.8 Å3 concurrent with continuous perovskite loss and lead iodide
growth. Oxygen-containing gases increase the reaction rates without
materially altering perovskite structural changes. Under the same
temperature and irradiation conditions in vacuo,
a self-healing reaction is observed, exhibited by a reproducible (0.9
± 0.3 Å3) lattice expansion and stabilization
of the perovskite. Interactions between the perovskite, defects, and
minority phases are simulated by generalized gradient approximation
Perdew–Burke–Ernzerhof (GGA-PBE) density functional
theory. Lattice contraction indicates an increase in the concentration
of Schottky defectspairs of formamidinium and iodine vacancies.
Under irradiation in every atmospheric condition, a solid solution
of Schottky defects with a concentration of several percent diffuses
and precipitates forming lead iodide and consuming the defects. In
the presence of ionized gases, this framework is modified to include
the continual loss of formamidinium and iodine ions from the perovskite
forming Schottky defects.