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Title: Lattice dynamics and the nature of structural transitions in organolead halide perovskites

Abstract

Organolead halide perovskites are a family of hybrid organic-inorganic compounds whose remark- able optoelectronic properties have been under intensive scrutiny in recent years. Here we use inelastic X-ray scattering to study low-energy lattice excitations in single crystals of methylammonium lead iodide and bromide perovskites. Our ndings conrm the displacive nature of the cubic-to- tetragonal phase transition, which is further shown, using neutron and x-ray diraction, to be close to a tricritical point. The experimental sound speed, around 100-200 m/s, suggests that electron- phonon scattering is likely a limiting factor for further improvements in carrier mobility. Lastly, we detect quasistatic symmetry-breaking nanodomains persisting well into the high-temperature cubic phase, possibly stabilized by local defects. These ndings reveal key structural properties of these materials, but also bear important implications for carrier dynamics across an extended temperature range relevant for photovoltaic applications.

Authors:
 [1];  [2];  [3];  [4];  [5];  [6];  [6];  [1];  [1];  [7];  [1]
  1. Univ. of Toronto, ON (Canada). Dept. of Electrical and Computer Engineering
  2. DuPont Central Research and Development, Wilmington, DE (United States); Univ. of Delaware, Newark, DE (United States). Dept. of Physics and Astronomy
  3. Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
  4. DuPont Electronics and Communication Technologies, Wilmington, DE (United States)
  5. DuPont Central Research and Development, Wilmington, DE (United States)
  6. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical and Engineering Materials Division
  7. Carnegie Mellon Univ., Pittsburgh, PA (United States). Dept. of Mechanical Engineering
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
Sponsoring Org.:
Natural Sciences and Engineering Research Council of Canada (NSERC); USDOE Office of Science (SC)
OSTI Identifier:
1328290
Grant/Contract Number:
AC05-00OR22725; AC02-06CH11357
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 94; Journal Issue: 9; Journal ID: ISSN 2469-9950
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Comin, Riccardo, Crawford, Michael K., Said, Ayman H., Herron, Norman, Guise, William E., Wang, Xiaoping, Whitfield, Pamela S., Jain, Ankit, Gong, Xiwen, McGaughey, Alan J. H., and Sargent, Edward H.. Lattice dynamics and the nature of structural transitions in organolead halide perovskites. United States: N. p., 2016. Web. doi:10.1103/PhysRevB.94.094301.
Comin, Riccardo, Crawford, Michael K., Said, Ayman H., Herron, Norman, Guise, William E., Wang, Xiaoping, Whitfield, Pamela S., Jain, Ankit, Gong, Xiwen, McGaughey, Alan J. H., & Sargent, Edward H.. Lattice dynamics and the nature of structural transitions in organolead halide perovskites. United States. doi:10.1103/PhysRevB.94.094301.
Comin, Riccardo, Crawford, Michael K., Said, Ayman H., Herron, Norman, Guise, William E., Wang, Xiaoping, Whitfield, Pamela S., Jain, Ankit, Gong, Xiwen, McGaughey, Alan J. H., and Sargent, Edward H.. 2016. "Lattice dynamics and the nature of structural transitions in organolead halide perovskites". United States. doi:10.1103/PhysRevB.94.094301. https://www.osti.gov/servlets/purl/1328290.
@article{osti_1328290,
title = {Lattice dynamics and the nature of structural transitions in organolead halide perovskites},
author = {Comin, Riccardo and Crawford, Michael K. and Said, Ayman H. and Herron, Norman and Guise, William E. and Wang, Xiaoping and Whitfield, Pamela S. and Jain, Ankit and Gong, Xiwen and McGaughey, Alan J. H. and Sargent, Edward H.},
abstractNote = {Organolead halide perovskites are a family of hybrid organic-inorganic compounds whose remark- able optoelectronic properties have been under intensive scrutiny in recent years. Here we use inelastic X-ray scattering to study low-energy lattice excitations in single crystals of methylammonium lead iodide and bromide perovskites. Our ndings conrm the displacive nature of the cubic-to- tetragonal phase transition, which is further shown, using neutron and x-ray diraction, to be close to a tricritical point. The experimental sound speed, around 100-200 m/s, suggests that electron- phonon scattering is likely a limiting factor for further improvements in carrier mobility. Lastly, we detect quasistatic symmetry-breaking nanodomains persisting well into the high-temperature cubic phase, possibly stabilized by local defects. These ndings reveal key structural properties of these materials, but also bear important implications for carrier dynamics across an extended temperature range relevant for photovoltaic applications.},
doi = {10.1103/PhysRevB.94.094301},
journal = {Physical Review B},
number = 9,
volume = 94,
place = {United States},
year = 2016,
month = 9
}

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  • Cited by 3
  • Organolead halide perovskites are a family of hybrid organic-inorganic compounds whose remarkable optoelectronic properties have been under intensive scrutiny in recent years. Here we use inelastic x-ray scattering to study low-energy lattice excitations in single crystals of methylammonium lead iodide and bromide perovskites. Our findings confirm the displacive nature of the cubic-to-tetragonal phase transition, which is further shown, using neutron and x-ray diffraction, to be close to a tricritical point. Lastly, we detect quasistatic symmetry-breaking nanodomains persisting well into the high-temperature cubic phase, possibly stabilized by local defects. These findings reveal key structural properties of these materials, and also bearmore » important implications for carrier dynamics across an extended temperature range relevant for photovoltaic applications.« less
  • Organolead mixed-halide perovskites such as CH 3NH 3PbX 3–aX' a (X, X' = I, Br, Cl) are interesting semiconductors because of their low cost, high photovoltaic power conversion efficiencies, enhanced moisture stability, and band gap tunability. Using a combination of optical absorption spectroscopy, powder X-ray diffraction (XRD), and, for the first time, 207Pb solid state nuclear magnetic resonance (ssNMR), we probe the extent of alloying and phase segregation in these materials. Because 207Pb ssNMR chemical shifts are highly sensitive to local coordination and electronic structure, and vary linearly with halogen electronegativity and band gap, this technique can provide the truemore » chemical speciation and composition of organolead mixed-halide perovskites. We specifically investigate samples made by three different preparative methods: solution phase synthesis, thermal annealing, and solid phase synthesis. 207Pb ssNMR reveals that nonstoichiometric dopants and semicrystalline phases are prevalent in samples made by solution phase synthesis. We show that these nanodomains are persistent after thermal annealing up to 200 °C. Further, a novel solid phase synthesis that starts from the parent, single-halide perovskites can suppress phase segregation but not the formation of dopants. Our observations are consistent with the presence of miscibility gaps and spontaneous spinodal decomposition of the mixed-halide perovskites at room temperature. This underscores how strongly different synthetic procedures impact the nanostructuring and composition of organolead halide perovskites. In conclusion, better optoelectronic properties and improved device stability and performance may be achieved through careful manipulation of the different phases and nanodomains present in these materials.« less
  • Carrier dynamics in methylammonium lead halide (CH3NH3PbI3-xClx) perovskite thin films, of differing crystal morphology, are examined as functions of temperature and excitation wavelength. At room temperature, long-lived (> nanosecond) transient absorption signals indicate negligible carrier trapping. However, in measurements of ultrafast photoluminescence excited at 400 nm, a heretofore unexplained, large amplitude (50%-60%), 45 ps decay process is observed. This feature persists for temperatures down to the orthorhombic phase transition. Varying pump photon energy reveals that the fast, band-edge photoluminescence (PL) decay only appears for excitation >= 2.38 eV (520 nm), with larger amplitudes for higher pump energies. Lower photon-energy excitationmore » yields slow dynamics consistent with negligible carrier trapping. Further, sub-bandgap two-photon pumping yields identical PL dynamics as direct absorption, signifying sensitivity to the total deposited energy and insensitivity to interfacial effects. Together with first principles electronic structure and ab initio molecular dynamics calculations, the results suggest the fast PL decay stems from excitation of high energy phonon modes associated with the organic sub-lattice that temporarily enhance wavefunction overlap within the inorganic component owing to atomic displacement, thereby transiently changing the PL radiative rate during thermalization. Hence, the fast PL decay relates a characteristic organic-to-inorganic sub-lattice equilibration timescale at optoelectronic-relevant excitation energies.« less