TY - GEN A1 - Breternitz, Joachim A1 - Lehmann, Frederike A1 - Barnett, Sarah A. A1 - Nowell, Harriott A1 - Schorr, Susan T1 - Role of the Iodide-methylammonium interaction in the ferroelectricity of CH3NH3PbI3 T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Excellent conversion efficiencies of over 20% and facile cell production have placed hybrid perovskites at the forefront of novel solar cell materials, with CH3NH3PbI3 being an archetypal compound. The question why CH3NH3PbI3 has such extraordinary characteristics, particularly a very efficient power conversion from absorbed light to electrical power, is hotly debated, with ferroelectricity being a promising candidate. This does, however, require the crystal structure to be non-centrosymmetric and we herein present crystallographic evidence as to how the symmetry breaking occurs on a crystallographic and, therefore, long-range level. Although the molecular cation CH3NH3+ is intrinsically polar, it is heavily disordered and this cannot be the sole reason for the ferroelectricity. We show that it, nonetheless, plays an important role, as it distorts the neighboring iodide positions from their centrosymmetric positions. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1196 KW - ferroelectricity KW - hybrid perovskites KW - inorganic chemistry KW - photovoltaic materials KW - structure elucidation Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-518227 SN - 1866-8372 IS - 1 ER - TY - JOUR A1 - Breternitz, Joachim A1 - Lehmann, Frederike A1 - Barnett, Sarah A. A1 - Nowell, Harriott A1 - Schorr, Susan T1 - Role of the Iodide-methylammonium interaction in the ferroelectricity of CH3NH3PbI3 JF - Angewandte Chemie - international edition N2 - Excellent conversion efficiencies of over 20% and facile cell production have placed hybrid perovskites at the forefront of novel solar cell materials, with CH3NH3PbI3 being an archetypal compound. The question why CH3NH3PbI3 has such extraordinary characteristics, particularly a very efficient power conversion from absorbed light to electrical power, is hotly debated, with ferroelectricity being a promising candidate. This does, however, require the crystal structure to be non-centrosymmetric and we herein present crystallographic evidence as to how the symmetry breaking occurs on a crystallographic and, therefore, long-range level. Although the molecular cation CH3NH3+ is intrinsically polar, it is heavily disordered and this cannot be the sole reason for the ferroelectricity. We show that it, nonetheless, plays an important role, as it distorts the neighboring iodide positions from their centrosymmetric positions. Y1 - 2019 VL - 59 IS - 1 PB - John Wiley & Sons, Inc. CY - New Jersey ER - TY - JOUR A1 - Franz, Alexandra A1 - Többens, Daniel M. A1 - Lehmann, Frederike A1 - Kärgell, Martin A1 - Schorr, Susan T1 - The influence of deuteration on the crystal structure of hybrid halide perovskites: a temperature-dependent neutron diffraction study of FAPbBr(3) JF - Acta crystallographica; Section B, Structural science, crystal engineering and materials N2 - This paper discusses the full structural solution of the hybrid perovskite formamidinium lead tribromide (FAPbBr(3)) and its temperature-dependent phase transitions in the range from 3 K to 300 K using neutron powder diffraction and synchrotron X-ray diffraction. Special emphasis is put on the influence of deuteration on formamidinium, its position in the unit cell and disordering in comparison to fully hydrogenated FAPbBr(3). The temperature-dependent measurements show that deuteration critically influences the crystal structures, i.e. results in partially-ordered temperature-dependent structural modifications in which two symmetry-independent molecule positions with additional dislocation of the molecular centre atom and molecular angle inclinations are present. KW - hybrid perovskite KW - FAPbBr(3) KW - deuteration KW - neutron powder diffraction KW - crystal structure Y1 - 2020 U6 - https://doi.org/10.1107/S2052520620002620 SN - 2052-5206 VL - 76 IS - 2 SP - 267 EP - 274 PB - Wiley-Blackwell CY - Oxford [u.a.] ER - TY - GEN A1 - Lehmann, Frederike A1 - Binet, Silvia A1 - Franz, Alexandra A1 - Taubert, Andreas A1 - Schorr, Susan T1 - Cation and anion substitutions in hybrid perovskites BT - solubility limits and phase stabilizing effects T2 - 7th World Conference on Photovoltaic Energy Conversion (WCPEC) (A Joint Conference of 45th IEEE PVSC, 28th PVSEC & 34th EU PVSEC) N2 - Organic or inorganic (A) metal (M) halide (X) perovskites (AMX(3)) are semiconductor materials setting the basis for the development of highly efficient, low-cost and multijunction solar energy conversion devices. The best efficiencies nowadays are obtained with mixed compositions containing methylammonium, formamidinium, Cs and Rb as well as iodine, bromine and chlorine as anions. The understanding of fundamental properties such as crystal structure and its effect on the band gap, as well as their phase stability is essential. In this systematic study X-ray diffraction and photoluminescense spectroscopy were applied to evaluate structural and optoelectronic properties of hybrid perovskites with mixed compositions. Y1 - 2018 SN - 978-1-5386-8529-7 U6 - https://doi.org/10.1109/PVSC.2018.8547645 SN - 2159-2330 SN - 2159-2349 SP - 1555 EP - 1558 PB - IEEE CY - New York ER - TY - JOUR A1 - Lehmann, Frederike A1 - Franz, Alexandra A1 - Toebbens, Daniel M. A1 - Levcenco, Sergej A1 - Unold, Thomas A1 - Taubert, Andreas A1 - Schorr, Susan T1 - The phase diagram of a mixed halide (Br, I) hybrid perovskite obtained by synchrotron X-ray diffraction JF - RSC Advances N2 - By using synchrotron X-ray powder diffraction, the temperature dependent phase diagram of the hybrid perovskite tri-halide compounds, methyl ammonium lead iodide (MAPbI3, MA+ = CH3NH3+) and methyl ammonium lead bromide (MAPbBr3), as well as of their solid solutions, has been established. The existence of a large miscibility gap between 0.29 ≤ x ≤ 0.92 (±0.02) for the MAPb(I1−xBrx)3 solid solution has been proven. A systematic study of the lattice parameters for the solid solution series at room temperature revealed distinct deviations from Vegard's law. Furthermore, temperature dependent measurements showed that a strong temperature dependency of lattice parameters from the composition is present for iodine rich compositions. In contrast, the bromine rich compositions show an unusually low dependency of the phase transition temperature from the degree of substitution. Y1 - 2019 U6 - https://doi.org/10.1039/c8ra09398a SN - 2046-2069 VL - 9 IS - 20 SP - 11151 EP - 11159 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Schuck, Götz A1 - Lehmann, Frederike A1 - Ollivier, Jacques A1 - Mutka, Hannu A1 - Schorr, Susan T1 - Influence of chloride substitution on the rotational dynamics of methylammonium in MAPbI(3-x)Cl(x) perovskites JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - Hybrid halide perovskites, MAPbI(3), MAPbI(2.94)Cl(0.0)6, and MAPbCl(3) (MA, methylammonium), were investigated using inelastic and quasielastic neutron scattering (QENS) with the aim of elucidating the impact of chloride substitution on the rotational dynamics of MA. In this context, we discuss the influence of the inelastic neutron scattering caused by low-energy phonons on QENS, resulting from the MA rotational dynamics in MAPbI(3-x)Cl(x). Through a comparative temperature-dependent QENS investigation with different energy resolutions, which allow a wide Fourier time window, we achieved a consistent description of the influence of chlorine substitution in MAPbI(3) on the MA dynamics. Our results showed that chlorine substitution in the low-temperature orthorhombic phase leads to a weakening of the hydrogen bridge bonds, since the characteristic relaxation times of C-3 rotation at 70 K in MAPbCl(3) (135 ps) and MAPbI(2.94)Cl(0.06) (485 ps) are much shorter than that in MAPbI(3) (1635 ps). For the orthorhombic phase, we obtained the activitin energies from the temperature-dependent characteristic relaxation times tau (c3). by Arrhenius fits, indicating lower values of E-a for MAPbCl(3) and MAPbI(2.94)Cl(0.06) compared to that of MAPbI(3). We also performed QENS analyses at 190 K for all three samples. Here, we observed that MAPbCI(3) shows slower MA rotational dynamics than MAPbI(3) in the disordered structure. Y1 - 2019 U6 - https://doi.org/10.1021/acs.jpcc.9b01238 SN - 1932-7447 VL - 123 IS - 18 SP - 11436 EP - 11446 PB - American Chemical Society CY - Washington ER -