CH 3 NH 3 PbI 3 : precise structural consequences of water absorption at ambient conditions

The crystal structure of the pristine (I) and aged (II) crystals of CH 3 NH 3 PbI 3 (hereafter MAPbI 3 ) hybrid organic–inorganic lead iodide has been studied at 293 K with high‐precision single‐crystal X‐ray diffraction using a synchrotron light source. We show that (I) and (II) are characterized by an identical tetragonal unit cell but different space groups: I 422 for (I) and P 4 2 2 1 2 for (II). Both space groups are subgroups of I 4/ mcm , which is widely used for MAPbI 3 . The main difference between (I) and (II) comes from the difference in hydrogen bonds between the MA + cation and the PbI 3 framework which is the direct consequence of H 2 O insertion in the aged crystal (II).