2019/12/26 by M. Songvilay, Zitian Wang, Victoria García Sakai +11 · 1 citation
Chemistry · Engineering · Materials Science · Physics and Astronomy · #Chemistry #Computational chemistry #Crystal structure #Crystallography #Halide #Halogen #Hydrogen bond #Inorganic chemistry #Materials science #Molecular dynamics #Molecule #Neutron #Neutron diffraction #Neutron scattering #Neutron spectroscopy #Organic and Molecular Conductors Research #Organic chemistry #Orthorhombic crystal system #Perovskite Materials and Applications #Physical chemistry #Physics #Solid-state spectroscopy and crystallography #Spectroscopy #Tetragonal crystal system #cond-mat.mtrl-sci
paper · pdf · doi:10.1103/physrevmaterials.3.125406
published as Phys. Rev. Materials 3, 125406 (2019) · (10 pages, 5 figures, to be published in Physical Review Materials)
arxiv created 2019/12/26 · openalex created_date 2019/12/26 · openalex publication_date 2019/12/30 · arxiv updated 2020/01/01 · openalex updated_date 2026/08/05
The organic-inorganic lead-halide perovskites are composed of organic molecules imbedded in an inorganic framework. The compounds with general formula CH3NH3PbX3 (MAPbX3) display large photovoltaic efficiencies for halogens X=Cl, Br, and I in a wide variety of sample geometries and preparation methods. The organic cation and inorganic framework are bound by hydrogen bonds that tether the molecules to the halide anions, and this has been suggested to be important to the optoelectronic properties. We have studied the effects of this bonding using time-of-flight neutron spectroscopy to measure the molecular dynamics in CH3NH3PbCl3 (MAPbCl3). Low-energy/high-resolution neutron backscattering reveals thermally activated molecular dynamics with a characteristic temperature of \ensuremath∼95 K. At this same temperature, higher-energy neutron spectroscopy indicates the presence of an anomalous broadening in energy (reduced lifetime) associated with the molecular vibrations. By contrast, neutron powder diffraction shows that a spatially long-range structural phase transitions occurs at 178 K (cubic \ensuremath→ tetragonal) and 173 K (tetragonal \ensuremath→ orthorhombic). The large difference between these two temperature scales suggests that the molecular and inorganic lattice dynamics in MAPbCl3 are actually decoupled. With the assumption that underlying physical mechanisms do not change with differing halogens in the organic-inorganic perovskites, we speculate that the energy scale most relevant to the photovoltaic properties of the lead-halogen perovskites is set by the lead-halide bond, not by the hydrogen bond.