title: Structures, Phase Transitions and Tricritical Behavior of the Hybrid Perovskite Methyl Ammonium Lead Iodide.
abstract: We have examined the crystal structures and structural phase transitions of the deuterated, partially deuterated and hydrogenous organic-inorganic hybrid perovskite methyl ammonium lead iodide (MAPbI3) using time-of-flight neutron and synchrotron X-ray powder diffraction. Near 330 K the high temperature cubic phases transformed to a body-centered tetragonal phase. The variation of the order parameter Q for this transition scaled with temperature T as Q ∼ (Tc-T)β, where Tcis the critical temperature and the exponent β was close to ¼, as predicted for a tricritical phase transition. However, we also observed coexistence of the cubic and tetragonal phases over a range of temperature in all cases, demonstrating that the phase transition was in fact first-order, although still very close to tricritical. Upon cooling further, all the tetragonal phases transformed into a low temperature orthorhombic phase around 160 K, again via a first-order phase transition. Based upon these results, we discuss the impact of the structural phase transitions upon photovoltaic performance of MAPbI3based solar cells.
authors: Chemical and Engineering Materials Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors: P S
authors: PS
authors: Whitfield
authors: DuPont Electronics and Communication Technologies, Wilmington, DE 19803, USA.
authors: N
authors: N
authors: Herron
authors: DuPont Central Research &Development, Wilmington, DE 19803, USA.|Advanced Photon Source, Argonne National Laboratory, 9700 S. Cass Avenue, Lemont, IL 60439, USA.
authors: W E
authors: WE
authors: Guise
authors: Chemical and Engineering Materials Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors: K
authors: K
authors: Page
authors: Chemical and Engineering Materials Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors: Y Q
authors: YQ
authors: Cheng
authors: DuPont Central Research &Development, Wilmington, DE 19803, USA.
authors: I
authors: I
authors: Milas
authors: DuPont Central Research &Development, Wilmington, DE 19803, USA.|Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA.
authors: M K
authors: MK
authors: Crawford