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Manipulating efficient light emission in two-dimensional perovskite crystals by pressure-induced anisotropic deformation

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Science Advances  26 Jul 2019:
Vol. 5, no. 7, eaav9445
DOI: 10.1126/sciadv.aav9445
  • Fig. 1 Schematics of the experiment and optical emission behavior of the 2D perovskite (PEA)2PbI4 under high pressure.

    (A) Illustration of DAC and the mechanism of hydrostatic compression. (B) A set of fluorescent microscopic images of a (PEA)2PbI4 crystal taken at the same lamp power. A bright-field image of the sample is presented in the center, surrounded by fluorescent images corresponding to different pressures. At 0 to 3.5 GPa, the fluorescence of (PEA)2PbI4 is equally bright, and the color is reversible by decompression. After 3.5 GPa, the fluorescence rapidly disappears and loses the reversibility. LP, low pressure; HP, high pressure.

  • Fig. 2 Spectroscopic measurements of 2D perovskite (PEA)2PbI4 under high pressure.

    The dotted arrows in all panels point to the direction of increasing pressure. (A) PL spectra excited by 2.62-eV (473-nm) blue laser. The last few spectra when pressure exceeds 4.5 GPa look flat due to low intensity. Intensity axis shows real counts per second (cps) as excitation power is fixed. (B) Zoom-in of PL spectra at pressure ranging from 4.5 to 7.6 GPa. arb. units, arbitrary units. (C) Raman spectra excited by 1.96-eV (633-nm) laser (when emission is green) and 2.33-eV (532-nm) laser (when emission is red). (D) trPL spectra. The smooth lines are biexponential decay fittings of the raw decay data.

  • Fig. 3 Analyses and evaluation of the optical properties and performances of 2D perovskite under pressure.

    (A) A typical set of excitation power–dependent PL spectra of 2D perovskite at 2.7 GPa. (B) Power-law fittings of power-dependent PL intensity of 2D perovskite at all pressures; the dotted arrow points to the direction of increasing pressure. (C) Pressure dependence of intensity coefficient and average PL lifetime of 2D perovskite. (D) Evolution of PL energy position and the corresponding relative quantum yield. The green trace shows the reversibility of the PL during decompression, which only happens in optical reversible region less than 3.5 GPa.

  • Fig. 4 Structural evolution and strongly anisotropic compression of (PEA)2PbI4 under pressure.

    All data are derived from XRD spectra and supported by first-principles calculation. (A) Synchrotron radiation XRD spectra of 2D perovskite under pressure. (B) Pressure dependence of unit cell volume. The volume change is represented in the form of V/V0, in which V0 is the initial volume at ambient pressure. The volume compression process is well fitted by Birch-Murnaghan equation. (C) Pressure dependence of the Pb─I bond length, which is slightly different in in-plane (<Pb─I>equatorial) and out-of-plane (<Pb─I>axial) directions. (D) Pressure dependence of unit cell parameters: a, b, and c. It is obvious that compression of c is visibly stronger than a and b, which are almost unchanged along pressure change. (E) Identical pressure dependence of a, b, and c is confirmed by first-principles calculation, which enhances the observation of anisotropic compression.

  • Fig. 5 Strongly anisotropic compression induced band structure change of (PEA)2PbI4.

    (A) Unit cell configuration under 0 and 4 GPa obtained from first-principles calculation. (B) Illustration of the compression and decompression process under hydrostatic high pressure. The springs represent the pairs of PEA molecules, which can elastically shrink and stretch, thus self-adapting to different pressures. (C) Schematic of a single type I quantum well with inorganic layer sandwiched by organic layers. Bound states exist in both the upper and bottom halves of the quantum well, stemming from the confinement of electrons and holes. (D) Projected density of states (PDOS) on each atom in (PEA)2PbI4 and the corresponding band structures at 0 and 4 GPa. The band structure diagram is shown in a particular symmetry direction along L-Γ-Z to emphasize the bandgap. The full version can be seen at fig. S3. (E) The energy positions of bound states as functions of barrier potential. The first and second bound states E1 and H1 are in orange and cyan, and E2 and H2 are in gray. (F) The pressure dependence of the barrier potential (Ue and Uh are in orange and cyan traces) and the weakening of quantum confinement (black trace).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/7/eaav9445/DC1

    Section S1. Calibration of pressure using emission line of ruby sphere

    Section S2. Crystal quality and layer orientation of (PEA)2PbI4 flake

    Section S3. Band structure and bandgap evolution under pressure

    Section S4. Analyses of the quantum confinement effects under pressure

    Section S5. The reversibility of (PEA)2PbI4 under pressure revealed by Raman spectra

    Section S6. The fitting of the trPL spectra under different pressures

    Section S7. The enhancement of exciton radiative recombination

    Section S8. The lattice angles of (PEA)2PbI4 under different pressures

    Section S9. The quantitative analyses of the [PbI6]4− octahedral distortion and rotation

    Fig. S1. The selected PL spectra of ruby sphere under different pressures.

    Fig. S2. SEM images on the section view of a typical as-grown crystal of (PEA)2PbI4.

    Fig. S3. The first-principles calculation of band structure and bandgap evolution.

    Fig. S4. Pressure dependence of effective mass of electron and hole in (PEA)2PbI4.

    Fig. S5. The optical micrographs of the (PEA)2PbI4 crystal inside DAC under different pressures.

    Fig. S6. The low–wave number Raman spectra and peak shift of (PEA)2PbI4 under different pressures.

    Fig. S7. The temperature-dependent PL spectra of (PEA)2PbI4.

    Fig. S8. The biexponential fitting of the trPL spectra of (PEA)2PbI4 under different pressures.

    Fig. S9. The lattice angles of (PEA)2PbI4 under different pressures.

    Fig. S10. The octahedral distortion and rotation evaluated by synchrotron radiation XRD and first-principles calculation.

    Table S1. The fitting parameters of trPL and calculated average PL lifetime.

    Movie S1. A video displaying the lattice structure evolution under pressure.

  • Supplementary Materials

    The PDF file includes:

    • Section S1. Calibration of pressure using emission line of ruby sphere
    • Section S2. Crystal quality and layer orientation of (PEA)2PbI4 flake
    • Section S3. Band structure and bandgap evolution under pressure
    • Section S4. Analyses of the quantum confinement effects under pressure
    • Section S5. The reversibility of (PEA)2PbI4 under pressure revealed by Raman spectra
    • Section S6. The fitting of the trPL spectra under different pressures
    • Section S7. The enhancement of exciton radiative recombination
    • Section S8. The lattice angles of (PEA)2PbI4 under different pressures
    • Section S9. The quantitative analyses of the PbI64− octahedral distortion and rotation
    • Fig. S1. The selected PL spectra of ruby sphere under different pressures.
    • Fig. S2. SEM images on the section view of a typical as-grown crystal of (PEA)2PbI4.
    • Fig. S3. The first-principles calculation of band structure and bandgap evolution.
    • Fig. S4. Pressure dependence of effective mass of electron and hole in (PEA)2PbI4.
    • Fig. S5. The optical micrographs of the (PEA)2PbI4 crystal inside DAC under different pressures.
    • Fig. S6. The low–wave number Raman spectra and peak shift of (PEA)2PbI4 under different pressures.
    • Fig. S7. The temperature-dependent PL spectra of (PEA)2PbI4.
    • Fig. S8. The biexponential fitting of the trPL spectra of (PEA)2PbI4 under different pressures.
    • Fig. S9. The lattice angles of (PEA)2PbI4 under different pressures.
    • Fig. S10. The octahedral distortion and rotation evaluated by synchrotron radiation XRD and first-principles calculation.
    • Table S1. The fitting parameters of trPL and calculated average PL lifetime.

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    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). A video displaying the lattice structure evolution under pressure.

    Files in this Data Supplement:

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