Research ArticlePHYSICS

Molecular behavior of zero-dimensional perovskites

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Science Advances  15 Dec 2017:
Vol. 3, no. 12, e1701793
DOI: 10.1126/sciadv.1701793
  • Fig. 1 Electronic and optical properties of CsPbBr3 and Cs4PbBr6.

    (A and B) Optimized crystal structures. (C and D) Electronic bands and projected density of states (PDOS) calculated at the PBE and PBE + SOC levels (the zero of energy is defined by the VBM in both instances). (E and F) Calculated absorption spectra with and without accounting for electron-hole (e/h) pair interactions together with (see inset) the exciton wave functions (green area) corresponding to the excitonic peaks. a.u., arbitrary units.

  • Fig. 2 Ground-state and polaron band absorption.

    (A) Ground-state absorption of a single Cs4PbBr6 unit and its charged-state absorption for (B) positive and (C) negative polarons, as calculated at the TDDFT level, together with experimental absorption spectra of Cs4PbBr6 thin film (gray line). The spin density distributions are given in the insets.

  • Fig. 3 TA spectra and polaron kinetics.

    TA spectra of (A) Cs4PbBr6 and (B) Cs4PbBr3 thin films with different delay times at a photoexcitation wavelength of 310 nm. (C) Photoexcitation kinetics of the Cs4PbBr6 film probed at 600 nm about PIA (the solid blue line is the fit for the kinetics using a monoexponential function). (D) Simulated phonon-induced relaxation of the polaronic state (PS1 and PS2) of a single Cs4PbBr6 unit. The frontier molecular energy levels and charge density involved in the excited electron relaxations are given in the inset. HOMO, highest occupied molecular orbital; LUMO, lowest unoccupied molecular orbital; GS, ground-state.

  • Fig. 4 Polaron transport and localization.

    (A) Schematic of charge carrier hopping paths and dimer model for calculating the charge carrier mobility of 0D Cs4PbBr6. (B) Charge density distributions for a 2 × 2 × 2 Cs4PbBr6 supercell with shortened Pb–Br distances (positive polaron) and enlarged Pb–Br distances (negative polaron) within the central [PbBr6]4− octahedron. (C) Charge density mapping of CBM of the central octahedron at selected times (0, 0.01, 0.05, 0.1, 0.5, and 1.0 ps). The initial state at 0 ps was set as the negative-polaron state and had the longest Pb–Br bonds in the central octahedron. The selected Pb–Br bond lengths are indicated in each time delay.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/12/e1701793/DC1

    fig. S1. Experimental and calculated electrical conductivity of CsPbB3 and Cs4PbBr6.

    fig. S2. Charge density descriptions of Cs4PbBr6 supercell.

    fig. S3. Average Pb–Br bond length and orbital energy evolution.

    fig. S4. X-ray diffraction patterns of CsPbB3 and Cs4PbBr6 thin films.

    table S1. Calculated charge transfer parameters and mobility of the Cs4PbBr6 crystal.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Experimental and calculated electrical conductivity of CsPbB3 and Cs4PbBr6.
    • fig. S2. Charge density descriptions of Cs4PbBr6 supercell.
    • fig. S3. Average Pb–Br bond length and orbital energy evolution.
    • fig. S4. X-ray diffraction patterns of CsPbB3 and Cs4PbBr6 thin films.
    • table S1. Calculated charge transfer parameters and mobility of the Cs4PbBr6 crystal.

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