Research ArticleSOLAR ENERGY

Light-induced picosecond rotational disordering of the inorganic sublattice in hybrid perovskites

See allHide authors and affiliations

Science Advances  26 Jul 2017:
Vol. 3, no. 7, e1602388
DOI: 10.1126/sciadv.1602388
  • Fig. 1 Radial diffraction intensity plot as a function of scattering vector Q.

    Center inset: Atomic-scale structure of MAPbI3 with tetragonal phase and I4cm space group (dark green spheres denote I and red spheres denote Pb). Right inset: Schematic of femtosecond transmission electron diffraction setup with optical pump and electron probe, showing also the recorded two-dimensional diffraction image of the MAPbI3 perovskite thin film. a.u., arbitrary units; EMCCD, electron-multiplying charge-coupled device.

  • Fig. 2 Time-dependent changes in Bragg peak intensities and associated RMS displacements.

    (A) Peak intensity dynamics for different diffraction peaks showing Q-dependent peak intensity decay with similar time constants. Excitation is at 400 nm and corresponding to a carrier density of 2.3 × 1019/cm3. The solid curves are global fits. Global fitting results for other peaks are plotted in fig. S7. (B) Comparison of peak no. 7 decay between 400- and 700-nm pump with similar photoinduced carrier density. (C) Semilog plot of intensity change (signal averaged over a delay range of 40 to 75 ps) as a function of the squared scattering factor (Q2) for different excitation densities, showing a Debye-Waller–like response corresponding to an increase in the RMS displacements of the atoms. The solid lines are linear fits with y intercept forced to 0. (D) Comparison between experimental and theoretical RMS (Embedded Image in angstroms) displacements at different temperatures (ΔT is referenced to room temperature).

  • Fig. 3 Static and differential radial diffraction spectra at different time delays.

    Differential radial diffraction spectrum at t = 5 and 70 ps with a photoexcited carrier density of 2.3 × 1019/cm3. Inset: Time evolution of scattering integrated over four different Q ranges: Q1 = (2.1 to 2.6 Å−1), Q2 = (3.8 to 4.1 Å−1), Q3 = (5.1 to 5.3 Å−1), and Q4 = (6.1 to 6.8 Å−1). The solid curves are single exponential fits to each Q range with time constants of 20 (±2) ps, 25 (±5) ps, 9 (±3) ps, and 11 (±7) ps from low Q to high Q, respectively.

  • Fig. 4 Comparison between experimental and calculated differential PDF.

    (A) Differential PDF at different delay times with a carrier density of 4.5 × 1019/cm3. The black curve in the main panel is the calculated difference PDF from MD simulations equilibrated at temperatures 300 and 325 K (ΔT = 25 K), with additional fluctuations of iodine atoms 0.1 Å in magnitude, to simulate the photoactivation (see text for details). Left inset shows the time-dependent PDF dynamics at r = 4.6 (±0.1) Å corresponding to the I–I atomic distance under two excitation densities, as noted in the figure. The solid curves in the left inset are single exponential fits. Right inset is an illustration of the proposed I rotational disorder in one PbI6 octahedron. (B) Calculated PDF (solid line) at room temperature (300 K; left axis) and calculated difference PDF (dashed line) from MD simulations equilibrated at temperatures 300 and 325 K, without additional fluctuations, corresponding to pure thermal activation.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/7/e1602388/DC1

    Supplementary Text

    fig. S1. Overlay of simulated electron scattering pattern and the measured diffraction pattern.

    fig. S2. Transient absorption data and analysis for MAPbI3.

    fig. S3. Long-time dynamics for high-order Bragg peaks of perovskite thin films for two photoexcited carrier densities.

    fig. S4. Scanning electron microscopy images of thermally evaporated perovskite thin films on TEM grids, showing an averaged grain size of about 50 to 100 nm.

    fig. S5. Pump fluence dependence of Bragg peak 1 to 4 (markers) intensity decay and single exponential fits (gray lines) to peaks 3 and 4.

    fig. S6. Pump fluence dependence of Bragg peak 5 to 8 (markers) intensity decay and single exponential fits (gray lines) to each peak.

    fig. S7. Global fitting of time-dependent intensity for peaks not shown in Fig. 2.

    fig. S8. Gaussian fit peak center change as function of pump-probe time delay for two photoexcited carrier densities.

    fig. S9. Calculated PDF difference between MD simulation temperatures T = 400 K and T = 375 K.

    fig. S10. Differential PDF plots of gold polycrystalline thin film at different time delays.

    fig. S11. Differential PDF plots at long-time delays under excitation at 400 nm with a carrier density of 2.3 × 1019/cm3.

    fig. S12. Differential PDF plots at different time delays under excitation at 400 nm with a carrier density of 4.5 × 1019/cm3.

    fig. S13. Differential PDF plots at different time delays under excitation at 400 nm with a carrier density of 2.3 × 1019/cm3.

    fig. S14. Differential PDF plots at different time delays under excitation at 400 nm with a carrier density of 1.4 × 1019/cm3.

    fig. S15. Comparison between electron diffraction on MAPbI3 and PbI2 thin films.

    fig. S16. Absorption spectra of MAPbI3 and PbI2; PbI2 time-resolved diffraction response.

    fig. S17. Differential PDF plots of PbI2 thin films at different time delays.

    fig. S18. Temperature-dependent x-ray diffraction scans across the tetragonal-cubic phase transition in MAPbI3 (measured from crystalline powders).

    fig. S19. Zoom-in evolution of diffraction peaks across the tetragonal-cubic phase transition.

    fig. S20. Intensity of (211) reflection as a function of temperature showing gradual decrease in intensity during the tetragonal-cubic transition.

    fig. S21. Normalized changes in area for selected diffraction peaks shown in fig. S18 as a function of temperature.

    table S1. Index of diffraction peaks.

    table S2. Summary of carrier density, ΔT, mean square displacement, and Debye temperature.

    table S3. Summary of decay time constants in picoseconds from single exponential fits of individual peaks under different pump fluences.

    table S4. Gaussian fit peak centers for eight peaks.

    table S5. Calculated atomic RMS in angstroms at different temperatures.

    References (5256)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Text
    • fig. S1. Overlay of simulated electron scattering pattern and the measured diffraction pattern.
    • fig. S2. Transient absorption data and analysis for MAPbI3.
    • fig. S3. Long-time dynamics for high-order Bragg peaks of perovskite thin films for two photoexcited carrier densities.
    • fig. S4. Scanning electron microscopy images of thermally evaporated perovskite thin films on TEM grids, showing an averaged grain size of about 50 to 100 nm.
    • fig. S5. Pump fluence dependence of Bragg peak 1 to 4 (markers) intensity decay and single exponential fits (gray lines) to peaks 3 and 4.
    • fig. S6. Pump fluence dependence of Bragg peak 5 to 8 (markers) intensity decay and single exponential fits (gray lines) to each peak.
    • fig. S7. Global fitting of time-dependent intensity for peaks not shown in Fig. 2.
    • fig. S8. Gaussian fit peak center change as function of pump-probe time delay for two photoexcited carrier densities.
    • fig. S9. Calculated PDF difference between MD simulation temperatures T = 400 K and T = 375 K.
    • fig. S10. Differential PDF plots of gold polycrystalline thin film at different time delays.
    • fig. S11. Differential PDF plots at long-time delays under excitation at 400 nm with a carrier density of 2.3 × 1019/cm3.
    • fig. S12. Differential PDF plots at different time delays under excitation at 400 nm with a carrier density of 4.5 × 1019/cm3.
    • fig. S13. Differential PDF plots at different time delays under excitation at 400 nm with a carrier density of 2.3 × 1019/cm3.
    • fig. S14. Differential PDF plots at different time delays under excitation at 400 nm with a carrier density of 1.4 × 1019/cm3.
    • fig. S15. Comparison between electron diffraction on MAPbI3 and PbI2 thin films.
    • fig. S16. Absorption spectra of MAPbI3 and PbI2; PbI2 time-resolved diffraction response.
    • fig. S17. Differential PDF plots of PbI2 thin films at different time delays.
    • fig. S18. Temperature-dependent x-ray diffraction scans across the tetragonalcubic phase transition in MAPbI3 (measured from crystalline powders).
    • fig. S19. Zoom-in evolution of diffraction peaks across the tetragonal-cubic phase transition.
    • fig. S20. Intensity of (211) reflection as a function of temperature showing gradual decrease in intensity during the tetragonal-cubic transition.
    • fig. S21. Normalized changes in area for selected diffraction peaks shown in fig. S18 as a function of temperature.
    • table S1. Index of diffraction peaks.
    • table S2. Summary of carrier density, ΔT, mean square displacement, and Debye temperature.
    • table S3. Summary of decay time constants in picoseconds from single exponential fits of individual peaks under different pump fluences.
    • table S4. Gaussian fit peak centers for eight peaks.
    • table S5. Calculated atomic RMS in angstroms at different temperatures.
    • References (52–56)

    Download PDF

    Files in this Data Supplement:

Navigate This Article