Possible decomposition pathway of hybrid halide perovskites in
the presence of water. A water molecule, a, is required
to initiate the process with the decomposition being driven by the
phase changes of both hydrogen iodide, (b, soluble in
water) and the methylammonia (c, volatile and soluble
in water). This pathway results in the formation of a yellow solid,
which corresponds the experimentally observed PbI2, d.