Research ArticleAPPLIED PHYSICS

Origin of unusual bandgap shift and dual emission in organic-inorganic lead halide perovskites

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Science Advances  28 Oct 2016:
Vol. 2, no. 10, e1601156
DOI: 10.1126/sciadv.1601156
  • Fig. 1 Temperature-dependent emission characteristics of CH3NH3PbI3 (fluence = 2 μJ/cm2).

    (A) Normalized PL intensity of CH3NH3PbI3 as a function of temperature recorded from 15 to 300 K (spectra have been vertically shifted for clarity). (B) Position of the PL peaks corresponding to the low energy and the orthorhombic and tetragonal phases of CH3NH3PbI3 as a function of temperature. (C) FWHM of the PL peaks corresponding to the low energy and the orthorhombic and tetragonal phases of CH3NH3PbI3 as a function of temperature. Green solid line shows the fitting obtained by taking into account the temperature-independent inhomogeneous broadening (Γ0) and the interaction between charge carriers and longitudinal optical phonons (LO-phonons), as described by the Fröhlich Hamiltonian. (D) Absolute intensity of PL spectra corresponding to the low-energy emission peak and the orthorhombic and tetragonal phases of CH3NH3PbI3 as a function of temperature from 15 to 300 K.

  • Fig. 2 Fluence-dependent emission characteristics of CH3NH3PbI3 recorded at 15 and 300 K.

    (A) PL spectra of the low- and high-energy emission peaks as a function of fluence recorded at 15 K. (B) Position of the low- and high-energy emission peaks as a function of fluence recorded at 15 K. (C) Intensity of the low- and high-energy emission peaks as a function of fluence recorded at 15 K. (D) PL spectra of the tetragonal phase as a function of fluence recorded at 300 K. (E) Position of the tetragonal emission peak as a function of fluence recorded at 300 K. (F) Intensity of the tetragonal emission peak as a function of fluence recorded at 300 K.

  • Fig. 3 Time-resolved PL of CH3NH3PbI3 performed at 15 and 300 K.

    (A) Fluence-dependent time-resolved PL of the low-energy emission peak recorded at 15 K. (B) Charge carrier lifetime (τ10) in the low-energy emission peak decreases with increasing fluence recorded at 15 K. (C) Fluence-dependent time-resolved PL of the high-energy emission peak (orthorhombic phase) recorded at 15 K. (D) Charge carrier lifetime (τ1, faster component) in the high-energy emission peak (orthorhombic phase) increases with increasing fluence recorded at 15 K. (E) Fluence-dependent time-resolved PL of the tetragonal phase recorded at 300 K. (F) Charge carrier lifetime (τ10) decreases with increasing fluence in the tetragonal phase recorded at 300 K. (τ10, time at which the maximum PL intensity decreases by a factor of 10).

  • Fig. 4 Temperature-dependent emission characteristics of CH3NH3PbBr3 (A to C) and CH(NH2)2PbBr3 (D to F) perovskite (fluence = 3 μJ/cm2).

    (A) Normalized PL intensity of CH3NH3PbBr3 as a function of temperature. (B) FWHM of the low- and high-energy emission peaks of CH3NH3PbBr3 as a function of temperature. (C) Position of the low- and high-energy emission peaks of CH3NH3PbBr3 as a function of temperature. (D) Normalized PL intensity of CH(NH2)2PbBr3 as a function of temperature. (E) FWHM of the PL peak of CH(NH2)2PbBr3 as a function of temperature. (F) Position of the PL peak of CH(NH2)2PbBr3 as a function of temperature. [Note that because of better structural stability, CH(NH2)2PbBr3 was chosen over CH(NH2)2PbI3.]

  • Fig. 5 Classical MD simulations.

    (A) Snapshots extracted from the classical MD simulations at (a) 100 K and (b) 300 K. Panels (c), (d), and (e) show the configurations of the samples used in the first-principles electronic structure calculations of the MA-ordered and MA-disordered orthorhombic and the tetragonal systems, respectively. Periodic boundary conditions are applied to improve the visualization. (B) Eg as a function of the pseudocubic lattice parameter, a = Embedded Image (V, volume per stoichiometric unit) for the MA-ordered (black symbols) and MA-disordered (red symbols) orthorhombic systems and the tetragonal system (blue symbols). Eg of the orthorhombic systems is computed starting from the computational equilibrium lattice. Subsequently, the lattice is isotropically expanded over a range of ~0.2 Å. The Eg of the tetragonal phase is computed over the same range as a. Open and filled symbols are introduced to improve readability, highlighting the change in the Eg across the phase transition. For the orthorhombic systems, filled symbols refer to a lattice parameter over a range of ~0.05 Å, consistent with the literature (29). Filled symbols for the tetragonal system are used in the complementary range.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/10/e1601156/DC1

    fig. S1. Structural characterization of perovskite films.

    fig. S2. Scanning electron microscopy analysis of perovskite films.

    fig. S3. Streak camera image of the time-resolved PL measurements recorded from the CH3NH3PbI3 film sample at 15 and 300 K.

    fig. S4. Streak camera image of the time-resolved PL measurements recorded from the CH3NH3PbBr3 film sample at 15 and 300 K.

    fig. S5. Streak camera image of the time-resolved PL measurements recorded from the CH(NH2)2PbBr3 film sample at 15 and 300 K.

    fig. S6. Time-resolved PL of CH3NH3PbI3 as a function of temperature (fluence = 2 μJ/cm2).

    fig. S7. Time-resolved PL of CH3NH3PbBr3 as a function of temperature (fluence = 3 μJ/cm2).

    fig. S8. Time-resolved PL of CH(NH2)2PbBr3 as a function of temperature (fluence = 3 μJ/cm2).

    fig. S9. Structure of the ideal orthorhombic phase.

    fig. S10. Pb-I pair correlation function of the MA-ordered and MA-disordered domains of the orthorhombic system and of the tetragonal phase.

    fig. S11. VBM of the MA-ordered and MA-disordered orthorhombic systems and of the tetragonal system.

    fig. S12. Band structure of the ordered and random domains of the orthorhombic phase of CH3NH3PbI3.

    fig. S13. Scheme illustrating possible absorption, relaxation, and emission mechanisms at low temperature in CH3NH3PbI3 and CH3NH3PbBr3.

    fig. S14. Configurations of the samples used in the first-principles electronic structure calculations.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Structural characterization of perovskite films.
    • fig. S2. Scanning electron microscopy analysis of perovskite films.
    • fig. S3. Streak camera image of the time-resolved PL measurements recorded from the CH3NH3PbI3 film sample at 15 and 300 K.
    • fig. S4. Streak camera image of the time-resolved PL measurements recorded from the CH3NH3PbBr3 film sample at 15 and 300 K.
    • fig. S5. Streak camera image of the time-resolved PL measurements recorded from the CH(NH2)2PbBr3 film sample at 15 and 300 K.
    • fig. S6. Time-resolved PL of CH3NH3PbI3 as a function of temperature (fluence = 2 μJ/cm2).
    • fig. S7. Time-resolved PL of CH3NH3PbBr3 as a function of temperature (fluence = 3 μJ/cm2).
    • fig. S8. Time-resolved PL of CH(NH2)2PbBr3 as a function of temperature (fluence = 3 μJ/cm2).
    • fig. S9. Structure of the ideal orthorhombic phase.
    • fig. S10. Pb-I pair correlation function of the MA-ordered and MA-disordered domains of the orthorhombic system and of the tetragonal phase.
    • fig. S11. VBM of the MA-ordered and MA-disordered orthorhombic systems and of the tetragonal system.
    • fig. S12. Band structure of the ordered and random domains of the orthorhombic phase of CH3NH3PbI3.
    • fig. S13. Scheme illustrating possible absorption, relaxation, and emission mechanisms at low temperature in CH3NH3PbI3 and CH3NH3PbBr3.
    • fig. S14. Configurations of the samples used in the first-principles electronic structure calculations.

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