ReviewPEROVSKITES

Lead halide perovskites: Crystal-liquid duality, phonon glass electron crystals, and large polaron formation

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Science Advances  13 Oct 2017:
Vol. 3, no. 10, e1701469
DOI: 10.1126/sciadv.1701469

Figures

  • Fig. 1 Structure of CH3NH3PbX3 perovskite.

    It consists of a framework of corner-sharing lead (gray) halide (purple) octahedrals and the CH3NH3+ cation (black, blue, and white) in the nanocage.

  • Fig. 2 Structure of a PGEC, Ba8Ga16Ge30.

    (A) Two tetrakaidecahedron cages along the z direction consisting of anions and guest Ba2+ cation rattling against the anionic cage. (B) The cage (outer circles) and the symmetry-broken off-center guest atom compose an effective electric dipole moment (thick arrows), which is the vector sum of each dipole (thin arrows). Reprinted figure with permission from Takabatake et al. (32). Copyright 2014 by the American Physical Society.

  • Fig. 3 TR-OKE probes liquid-like motions in lead halide perovskites.

    TR-OKE transients from single-crystal (A) CsPbBr3, (B) MAPbBr3, and (C) FAPbBr3. The pump-probe cross-correlation is depicted as gray [full width at half-maximum (FWHM), 70 fs]. The inset in (A) illustrates the experimental setup. From Zhu et al. (25). Reprinted with permission from AAAS.

  • Fig. 4 Low-frequency Raman spectra of hybrid and inorganic lead halide perovskite crystals.

    MAPbBr3 (A) and CsPbBr3 (B) in the orthorhombic phase (blue), tetragonal phase (green), and cubic phase (red). Note that the phase transition temperatures for CsPbBr3 are much higher than those for MAPbBr3. The central peak characteristic of dynamic disordered, highly anharmonic, and dissipative vibrations grows with temperature in both materials. a.u., arbitrary units. Reprinted figure with permission from Yaffe et al. (24). Copyright 2017 by the American Physical Society.

  • Fig. 5 Temperature dependence of Hall mobility in single-crystal MAPbBr3.

    The fits to μHall (cm2 V−1 s−1) ∝ T (K)−γ give γ = 0.5 in the tetragonal phase and γ = 1.5 in the cubic phase. From Yi et al. (64). Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission.

  • Fig. 6 Calculated dielectric functions of MAPbBr3 (blue) and CsPbBr3 (red).

    The solid and dashed curves show the real, Re[ε] (left), and imaginary, Im[−1/ε] (right), parts, respectively. From/adapted from Miyata et al. (43). Copyright The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC) http://creativecommons.org/licenses/by-nc/4.0/.

  • Fig. 7 Phonon dynamics triggered by photo-carrier injection as a function of pump-probe delay observed by TR-OKE with across-gap excitation.

    The TR-OKE responses for MAPbBr3 (red circles) and CsPbBr3 (blue circles) were obtained with excitation photon energies of 2.30 and 2.38 eV, respectively. The lines are double-exponential fits convoluted with a Gaussian function, which describes cross-correlation between the pump and the probe pulse (gray; FWHM, 70 fs). From/adapted from Miyata et al. (43) Copyright The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC) http://creativecommons.org/licenses/by-nc/4.0/.

  • Fig. 8 Slow cooling of hot carriers in HOIPs.

    The data points are mean hot carrier energies from TR-2PPE of MAPbI3 thin films (red) (34) and TR-PL of MAPbBr3 single crystals (blue) (25). In the latter, a background offset due to intrinsic broadening in PL spectra has been subtracted. The excess excitation energy (above bandgap) is 1.0 eV for MAPbI3 and 0.8 eV for MAPbBr3.

  • Fig. 9 Excitation density dependence of excess electronic energy in MAPbI3.

    The data points are from TR-PL in the initial 0- to 20-ps time window (time resolution) of a vapor-deposited MAPbI3 thin film. PL at three excitation photon energies, hν = 3.06 eV (blue), 2.48 eV (green), and 2.15 eV (orange). The gray curve is an exponential fit to the data points. The y axis is excess electronic energy, referenced to the asymptotic value at long times (~0.5 ns). Reprinted (adapted) with permission from Niesner et al. (34). Copyright (2016) American Chemical Society.

  • Fig. 10 Excitation density–dependent photoconductivity shows little charge carrier trapping.

    (A) Photoconductivity measured in a vapor-grown 100-nm-thick polycrystalline CH3NH3PbI3 film as a function of absorbed photon density. (B) Photoconductivity measured as a function of incident photon flux in a macroscopic single-crystal CH3NH3PbBr3 with a (dark) Hall mobility μHall ≈ 60 cm2 V−1 s−1 (for holes). Dashed lines are the power law fits with exponent α = 1/2: σ ∝ Gα or Fα. Reprinted with permission from Chen et al. (58). Copyright (2016) Nature Commun.

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