Christians et al. also observed the formation of a hydrated
product after CH3NH3PbI3 was exposed to moisture [38]. This was
uncovered using XRD patterns, although, they strengthened the
argument of the existence of this compound by synthesising
(CH3NH3)4 PbI6 2H2O themselves. Interestingly, a video depicting
the formation of these hydrate crystals in water was included in
the supporting information of this paper [38]. The XRD pattern of
this compound was compared to that of a CH3NH3PbI3 film which
had been exposed to a RH of 90% for 7 days. Strong peaks existing
in the hydrate at 2θ values of 8.42° and 10.46° emerge in the
perovskite film after exposure to 90% RH. This provides a strong
argument for the formation of this intermediate hydrated compound
as CH3NH3PbI3 is exposed to water. The formation of this
hydrated compound caused a significant reduction in the film
absorption; however, transient absorption spectroscopy (TAS)
measurements revealed that the formation of the hydrate compound
did not influence the charge carrier dynamics on a short
time scale. The authors postulate that the formation of the
hydrated compound is dependent on the relative strength of the
hydrogen bonding interaction between either the cation
(CH3NH3
þ) or H2O with PbI6. Inherently strengthening the bond
between the cation and metal halide may improve the perovskites
resistance to moisture