Unravelling the Behavior of Dion–Jacobson Layered Hybrid Perovskites in Humid Environments

Layered hybrid halide
perovskites are known to be more environmentally
stable than their 3D analogues. The enhanced stability is particularly
relevant for Dion–Jacobson-type layered perovskites due to
their promising photovoltaic performances. However, in contrast to
the expected resilience to moisture, we reveal that the structure
of Dion–Jacobson perovskite phases based on a 1,4-phenylenedimethanammonium
spacer is disrupted in humid conditions using X-ray diffraction, UV–vis
spectroscopy, thermogravimetric analysis, and solid-state NMR spectroscopy.
The process takes place at ≥65 ± 5% relative humidity,
with a time scale on the order of minutes. The original layered structure
can be restored upon annealing and the hydration can be suppressed
by postsynthetic annealing in air, which is attributed to the generation
of a self-protective layer of PbI2. This study thereby
reveals a unique behavior of layered perovskites in humid environments,
which is critical to their stabilizing role in perovskite devices.