Extremely efficient internal exciton dissociation through edge states in layered 2D perovskites

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Science  24 Mar 2017:
Vol. 355, Issue 6331, pp. 1288-1292
DOI: 10.1126/science.aal4211
  • Fig. 1 Evidence of phase purity of the RPPs (n = 1 to 5) and comparison of optical properties of thin films and exfoliated crystals.

    (A) Schematics of the QW-like crystal structure showing perovskite layers in the plane (Embedded Image) sandwiched between organic spacing layers. (B) Phase purity established by monitoring the position and number of the low-angle peaks in x-ray diffraction patterns for each n value. a.u., arbitrary units. Absorption and PL of the thin films (C and D) and exfoliated crystals (E and F). (G) Optical band gap derived from absorption (open symbols) and PL (filled symbols) as a function of n. (Inset) Shift of the optical band gap in thin films with respect to exfoliated crystals (from absorption). (H) PL linewidth versus n, showing inhomogeneous broadening in thin films as compared with that of exfoliated crystals.

  • Fig. 2 Microscopic origin of the low-energy band gap in 2D perovskite thin films for n = 3.

    (A) PL-intensity map of a single exfoliated crystal, probed at 2.010 and 1.680 eV. (Right) Microscopy image showing the layer edges of the exfoliated crystal. Scale bar, 10 μm. (B) Comparison of the PL in the exfoliated crystal, at the exfoliated-crystal edges, and in the corresponding thin film. (C) PLE-integrated signal of the LES, measured by locally exciting the exfoliated-crystal edges. The measured PL profile of the LES is also plotted. (D) TRPL of the PL features X state and LES observed in (B) and (C). (E) Schematics of the photoabsorption and PL processes in 2D perovskite exfoliated crystals with n > 2.

  • Fig. 3 Optical absorption and emission mechanisms in thin films of 2D perovskites.

    (A) Thin film n = 3 absorption (green), PL at photoexcitation 100 mW/cm2 (black) and 106 mW/cm2 (red). (B) I0 dependence of the integrated PL. Dashed lines are fits to the data. (C) TRPL in the thin films n = 3. (Inset) Corresponding lifetimes (τ) of the X states and LESs as a function of the n value. Excitation at ~100 mW/cm2. (D) Schematics of the photoabsorption and PL processes in a 2D perovskite thin film with n > 2. In contrast to exfoliated crystals, thin-film perovskite layers are preferentially oriented normal to the substrate (fig. S10) (12, 17), therefore, excitation light probes numerous amounts of LESs. (E) Summary of the main photoemission mechanisms in thin films. The diffusion length was estimated from fig. S13 (17). VB and CB stand for valence and conduction bands, respectively.

  • Fig. 4 Figures of merit of thin-film devices for light-harvesting and solid-state emission.

    (A) J-V characteristics measured under AM1.5 illumination. (B) Power-conversion efficiency as a function of 2D perovskite n value (QW thickness). (C) EQE for the PV devices in (A). (D) PLQY in thin films as a function of n value for several light-excitation intensities.

Supplementary Materials

  • Extremely efficient internal exciton dissociation through edge states in layered 2D perovskites

    J.-C. Blancon, H. Tsai, W. Nie, C. C. Stoumpos, L. Pedesseau, C. Katan, M. Kepenekian, C. M. M. Soe, K. Appavoo, M. Y. Sfeir, S. Tretiak, P. M. Ajayan, M. G. Kanatzidis, J. Even, J. J. Crochet, A. D. Mohite

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