title: Mechanism of Pressure-Induced Phase Transitions, Amorphization, and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide.
abstract: Our single-crystal X-ray diffraction study of methylammonium lead triiodide, MAPbI3, provides the first comprehensive structural information on the tetragonal phase II in the pressure range to 0.35 GPa, on the cubic phase IV stable between 0.35 and 2.5 GPa, and on the isostructural cubic phase V observed above 2.5 GPa, which undergoes a gradual amorphization. The optical absorption study confirms that up to 0.35 GPa, the absorption edge of MAPbI3 is red-shifted, allowing an extension of spectral absorption. The transitions to phases IV and V are associated with the abrupt blue shifts of the absorption edge. The strong increase of the energy gap in phase V result in a spectacular color change of the crystal from black to red around 3.5 GPa. The optical changes have been correlated with the pressure-induced strain of the MAPbI3 inorganic framework and its frustration, triggered by methylammonium cations trapped at random orientations in the squeezed voids.
authors.affiliation: Faculty of Physics, Adam Mickiewicz University , Umultowska 85, 61-614 Poznań, Poland.
authors.forename: Marek
authors.initials: M
authors.lastname: Szafrański
authors.affiliation: Faculty of Chemistry, Adam Mickiewicz University , Umultowska 89b, 61-614 Poznań, Poland.
authors.forename: Andrzej
authors.initials: A
authors.lastname: Katrusiak