  Metal halide perovskites are known to suffer from rapid degradation, limiting
their direct applicability. Here, the degradation of phenethylammonium lead
iodide (PEA2PbI4) two-dimensional perovskites under ambient conditions is
studied using fluorescence, absorbance and fluorescence lifetime measurements.
It is demonstrated that a long-term stability of two-dimensional perovskites
can be achieved through the encapsulation with hexagonal boron nitride. While
un-encapsulated perovskite flakes degrade within hours, the encapsulated
perovskites are stable for at least three months. In addition, encapsulation
considerably improves the stability under laser irradiation. The environmental
stability, combined with the improved durability under illumination, is a
critical ingredient for thorough spectroscopic studies of the intrinsic
opto-electronic properties of this material platform.
