Reversing Organic–Inorganic Hybrid Perovskite Degradation in Water via pH and Hydrogen Bonds

The moisture instability
of organic–inorganic hybrid perovskite
solar cells has been a major obstacle to the commercialization, calling
for mechanistic understanding of the degradation process, which has
been under debate. Here we present a surprising discovery that the
degradation is actually reversible, via in situ observation of X-ray
diffraction, supported by FTIR and SEM. To isolate the hydrogen bond
effect, water was replaced by methanol during the in situ experiment,
revealing the decomposition to be initiated by the breakdown of N–H–I
hydrogen bonds. This is followed by the step of organic iodide hydrolyzing,
which can be inhibited in the neutral environment, making the whole
process reversible under variable pH.